TRW & Co · Competition, Regulatory & Investigations
NSIA Lawyers in London
NSIA lawyers in London help investors decide whether a deal must be cleared by the government before completion under the National Security and Investment Act 2021. The regime covers 17 sensitive sectors, applies to UK and overseas buyers alike and makes non-notified notifiable deals void. Planned 2026 changes will add water and reshape several sector definitions.
Key pointThe NSIA catches investors of every nationality, including UK buyers and internal reorganisations. A missed mandatory notification does not just risk a fine; it makes the acquisition legally void until validated.
At a glance
17 mandatory sectors
Acquisitions of control over entities in 17 sensitive areas, from energy and defence to AI and data infrastructure, need approval before completion.
Void if not approved
Completing a notifiable acquisition without approval makes it void and is a criminal offence, with civil penalties of up to 5% of worldwide turnover or £10 million.
Thirty-day review
Once a notification is accepted, the government has up to 30 working days to clear the deal or call it in for a fuller assessment.
Five-year call-in
The government can call in qualifying acquisitions up to five years after completion, and within six months of becoming aware of them.
Sector changes ahead
In March 2026 the government confirmed it will add water, separate critical minerals and semiconductors, and narrow the AI sector through new regulations.
Swipe or scroll →
What the National Security and Investment Act covers
The National Security and Investment Act 2021 (NSIA) gives the UK government power to screen, impose conditions on and block acquisitions that could harm national security. Investors instruct NSIA lawyers in London to decide whether a deal must be notified before completion, whether a voluntary notification is wise, and how screening risk should be built into the timetable and the transaction documents.
The regime came into force on 4 January 2022. It is administered by the Investment Security Unit (ISU) in the Cabinet Office, and the decision-maker is the Chancellor of the Duchy of Lancaster as the relevant Secretary of State. Unlike many foreign investment regimes, it applies to acquirers of any nationality, including UK investors and internal group reorganisations.
The Act has two limbs. A mandatory, suspensory regime applies to acquisitions of control over entities active in 17 sensitive areas of the economy. Alongside it, a call-in power lets the government review any qualifying acquisition of an entity or asset across the whole economy, whether or not it was notified. The NSIA lawyers in London investors use need to analyse both limbs on every relevant deal.
The statutory framework
The core provisions of the National Security and Investment Act 2021 are straightforward to locate, even if their application is not:
- Call-in power. Section 1 allows the Secretary of State to call in a trigger event for assessment where it may give rise to a risk to national security. Section 2 limits the power to six months from the government becoming aware of the acquisition and five years from completion.
- Trigger events. Section 8 sets out when a person gains control of an entity, and section 9 covers control of assets such as land, intellectual property and other property.
- Mandatory notification. Section 13 provides that a notifiable acquisition completed without approval is void, and section 14 sets out the mandatory notification procedure.
- Retrospective validation and voluntary notification. Sections 16 and 18 allow parties to apply for validation of a void acquisition and to notify voluntarily.
- Orders and offences. Sections 25 and 26 provide for interim and final orders. Section 32 makes completing a notifiable acquisition without approval a criminal offence.
The 17 mandatory sectors are defined in the Notifiable Acquisition Regulations, which are detailed and technical. The government's guidance on the 17 types of notifiable acquisition explains each sector, and its main guidance on acquisitions covers trigger events, timescales and process.
Interaction with merger control
The NSIA is separate from the Competition and Markets Authority's merger control regime under the Enterprise Act 2002. The Cabinet Office and the CMA have a published memorandum of understanding on coordination, and the Act includes provisions on how the two regimes interact. A deal may face both reviews, and our merger control team coordinates the two analyses.
Trigger events and the 17 sensitive sectors
A qualifying acquisition of an entity occurs when an acquirer's shareholding or voting rights cross a threshold: from 25% or less to more than 25%, from 50% or less to more than 50%, or from less than 75% to 75% or more. It also occurs where an acquirer gains voting rights that allow it to secure or prevent the passage of any class of resolution, or gains material influence over the entity's policy.
Mandatory notification is only required for acquisitions of qualifying entities carrying on specified activities in the 17 sectors, and only for the shareholding and voting-rights triggers. Material influence and asset acquisitions are not subject to mandatory notification, but they remain within the call-in power and can be notified voluntarily.
The 17 sectors are advanced materials, advanced robotics, artificial intelligence, civil nuclear, communications, computing hardware, critical suppliers to government, cryptographic authentication, data infrastructure, defence, energy, military and dual-use, quantum technologies, satellite and space technologies, suppliers to the emergency services, synthetic biology and transport. Each is defined by reference to particular activities rather than a general industry label, so a company in a sector may be outside the definitions while a company that does not see itself as "defence" or "AI" may be inside them.
Overseas entities and internal reorganisations
An entity formed outside the UK can be a qualifying entity if it carries on activities in the UK or supplies goods or services to people in the UK. The government's guidance on acquisitions outside the UK explains this test. Global deals with modest UK operations therefore still need analysis.
The government's guidance treats internal reorganisations as capable of being qualifying acquisitions, and of requiring mandatory notification, even where the ultimate beneficial owner does not change. The government has previously indicated that it may exempt certain reorganisations and insolvency appointments, but that change has not yet been made, so NSIA lawyers in London clients use will still check intra-group transfers.
Mandatory, voluntary or no notification
The key decision is which route applies and, where notification is optional, whether to use it. The table below summarises the options.
| Route | When it applies | Effect | Practical comment |
|---|---|---|---|
| Mandatory notification | Acquisition of control of a qualifying entity active in one of the 17 sectors, through a shareholding or voting-rights threshold | Must not complete before approval; completing without approval is void and an offence | Build approval in as a condition precedent with a realistic long-stop date |
| Voluntary notification | Any other qualifying acquisition, including material influence and asset deals, where there may be a national security interest | Once cleared, the government cannot later call in the deal on the same facts, save in limited cases such as false information | Gives certainty where the target has sensitive capabilities near the sector definitions |
| Retrospective validation | A notifiable acquisition completed without approval | The acquisition remains void until validated | Apply promptly; the government may also call in the acquisition |
| No notification | Qualifying acquisitions outside the 17 sectors with no realistic security dimension | Call-in remains possible for up to five years after completion | Record the reasoning in the deal file |
A voluntary notification adds time, so investors should weigh it against the risk of a call-in after completion, when unwinding is far more disruptive. NSIA lawyers in London deal teams appoint will consider the target's customers, data, technology, location near sensitive sites and the acquirer's ownership and links to foreign states.
Under the NSIA, a missed mandatory filing does not just risk a penalty. The acquisition is void, which can unravel the legal ownership of the business you paid for.
The screening process and timetable
Notifications are submitted through the government's online NSI notification service. The statutory count excludes weekends and public holidays in any part of the UK.
- Sector and trigger analysis. Map the target's activities against the Notifiable Acquisition Regulations and confirm which trigger event the transaction creates.
- Prepare the notification. Collect information on the acquirer's ownership chain, the target, the transaction and any links to foreign governments or sensitive activities.
- Acceptance. The ISU checks that the form is complete. An incomplete form is rejected with reasons and must be resubmitted.
- Review period. Once accepted, the government has up to 30 working days to clear the acquisition or issue a call-in notice.
- Assessment period. If called in, an initial period of 30 working days applies, extendable by an additional 45 working days and then by agreement. Information and attendance notices stop the clock during this period.
- Interim orders. During assessment, the government may impose interim orders, for example restricting information flows or integration.
- Final decision. The government either issues a final notification that no further action will be taken or makes a final order imposing conditions, blocking the deal or requiring it to be unwound. Notices of final orders are published.
Challenges to decisions under the Act are brought in the High Court, and section 49 imposes a short limitation period of 28 days, subject to exceptional circumstances. Where advocacy in the higher courts is required, we instruct specialist counsel.
Where a target is in financial distress, tell the ISU early and provide evidence. The government's guidance says it may expedite the decision on whether to call in a deal in exceptional circumstances, but it will expect to see analysis from restructuring advisers and evidence that other funding options are unavailable. Our restructuring team works on these cases.
Documents and information to assemble
A well-prepared notification reduces the risk of rejection and follow-up questions. The information required is detailed, and the ownership chain is often the slowest part. Typical inputs include:
- A complete ownership structure for the acquirer, up to the ultimate beneficial owners, including funds, general partners and limited partners with significant rights.
- Details of the target's activities in the UK, its products, customers (especially government and critical national infrastructure customers) and sites.
- Pre- and post-transaction shareholdings and voting rights, plus governance rights such as board seats and vetoes.
- Information on the acquirer's other investments in the same or related sectors, and any links to foreign governments.
- The transaction documents and expected timetable.
- Information about the target's sensitive technology, intellectual property and data holdings.
Providing false or misleading information is an offence under the Act and can lead to a decision being reopened, so accuracy matters more than speed.
Reforms announced in 2026
The government consulted in 2025 on updating the Notifiable Acquisition Regulations and published its response on 12 March 2026. It confirmed plans to add water as a new mandatory sector, to create standalone schedules for critical minerals and semiconductors, to narrow the artificial intelligence schedule so that routine users of off-the-shelf AI are excluded, and to make adjustments to communications, data infrastructure, energy and other schedules.
These changes require secondary legislation. At the time of writing, the current regulations remain in force, so deals must be assessed on the existing definitions while keeping an eye on what is coming. Transactions in data centres, water, mining supply chains and AI should build in flexibility. Our data centres and energy teams track the sector-specific changes, and our NSIA explainer sets out the current rules in plain English.
Risks and common mistakes
These are the errors NSIA lawyers in London most often see, and most can be avoided with early analysis.
Assuming UK or friendly-state investors are outside the regime
The NSIA applies to acquirers of any nationality, including British companies and investors from allied countries. The mandatory regime depends on the target's activities and the level of control acquired, not the buyer's identity. The acquirer's profile matters to the substantive assessment of risk, but it does not remove a filing obligation. Domestic private equity buyers and UK trade buyers should therefore run the same sector analysis as overseas investors.
Reading the sector definitions too broadly or too narrowly
The 17 sectors are defined by specific activities, often with technical language. A target that supplies software to a utility, holds a component patent or operates a data centre for third parties may be caught even though it does not describe itself as being in a sensitive sector. Conversely, filings are sometimes made unnecessarily because a name resembles a sector. The answer comes from reading the regulations and guidance against the target's actual operations, with input from the business.
Completing before approval
Completion of a notifiable acquisition without approval is void and an offence. Civil penalties can reach 5% of worldwide turnover or £10 million, whichever is greater, and individuals face criminal liability, with imprisonment of up to five years on indictment. Completion mechanics, escrow arrangements and conditions precedent should be drafted so that no part of the trigger event occurs before clearance, including staged share transfers and option exercises.
Overlooking minority investments and fund structures
Crossing 25% of voting rights in a sensitive-sector company is a mandatory trigger, even in a venture capital round. Fund structures can also create indirect acquisitions of control through a chain of holdings. Investors in technology businesses should map holdings across the cap table before each round. Our venture capital and private equity teams build this into investment documents.
Treating clearance as the end of the matter
Final orders can impose continuing conditions, such as restrictions on access to sensitive information, requirements for UK security-cleared personnel or supply commitments to the government. Breaching an order is an offence and can lead to civil penalties. Post-completion compliance needs an owner within the business, reporting lines and periodic review, especially after integration into a wider group.
Cross-border investment: Bangladesh, the Gulf, Asia and the EU
TRW & Co is headquartered in Dhaka with offices in Singapore, Dubai and China, and we often advise investors entering the UK from those markets. The NSIA does not treat any nationality as disqualifying, but the government assesses acquirer risk, including links to foreign states, so how an investor presents its ownership and governance matters.
- Bangladeshi investors. Groups expanding into UK manufacturing, energy or technology should map targets against the sectors before signing. Our Bangladeshi businesses in the UK page covers wider entry issues.
- Gulf sovereign and family capital. State-linked investors should expect detailed questions about governance, decision-making and the independence of the investing vehicle.
- Asian and Chinese investors. Acquisitions in technology, semiconductors and critical minerals receive close scrutiny. Early engagement and careful remedy design can be important.
- EU and other screening regimes. Many EU member states operate their own foreign investment screening, so multi-jurisdictional deals need a coordinated filing plan.
Sanctions and export controls also intersect with national security screening. Our sanctions and export controls team checks counterparties and technology transfers alongside the NSIA analysis.
How TRW & Co helps
TRW & Co's London office is authorised and regulated by the Solicitors Regulation Authority. We advise acquirers, targets, sellers and funds on the NSIA as part of transaction work and as stand-alone advice. NSIA lawyers in London should be able to give a fast, reasoned view on whether a filing is required, and that is where we start.
Filing analysis
We map the target's activities against the 17 sector definitions and the trigger events. Where there is uncertainty, we explain the risk of each route and record the reasoning.
Notifications and ISU engagement
We prepare mandatory, voluntary and retrospective validation notifications and handle questions from the ISU, including information notices during assessment.
Deal protection
We draft conditions precedent, long-stop dates, cooperation obligations and risk allocation for national security remedies. This aligns with our M&A, private equity and venture capital work.
Final orders and compliance
We negotiate conditions where the government has concerns and set up compliance programmes for continuing obligations after completion.
What to expect from NSIA lawyers in London
The first deliverable should be a short, reasoned memo: which sector definitions were considered, which trigger event applies and which notification route is recommended. That record protects the board if the deal is later questioned, and it gives lenders and co-investors the comfort they usually request before funding.
From there, the work is about timing. Experienced NSIA lawyers in London will prepare the notification in parallel with due diligence, so that the ownership information is ready when the transaction documents are signed and the review period starts as early as possible. They will also tell you candidly when a filing is not needed, so that time and management attention are not spent on unnecessary notifications.
See all our services on our practices page or learn about our M&A practice.
Checklist for decision-makers
- Confirm whether the target carries on activities in the UK or supplies goods or services to the UK.
- Map the target's activities against each of the 17 sector definitions, using the current regulations.
- Identify the trigger event: shareholding, voting rights, resolution rights, material influence or asset control.
- Check internal reorganisations and staged acquisitions for separate trigger events.
- Decide between mandatory, voluntary or no notification and record the reasoning.
- Build the review and assessment periods into the timetable and conditions.
- Prepare the acquirer's full ownership chain early.
- Coordinate with CMA merger control, overseas screening and sanctions checks.
- Track the 2026 sector changes for water, critical minerals, semiconductors and AI.
To discuss a transaction, contact our London office at Holborn Gate, 330 High Holborn, London WC1V 7QH, at info@trw.co or on +880 1779 127165.
Frequently asked questions
01Does the NSIA apply to UK investors?
Yes. The National Security and Investment Act 2021 applies to acquirers of any nationality, including UK companies, funds and individuals. Mandatory notification depends on the target's activities in the 17 sensitive sectors and on the level of control acquired, not the buyer's nationality. The acquirer's identity is relevant to whether the government sees a national security risk, but a UK buyer of a qualifying entity in a mandatory sector must still notify and obtain approval before completing.
02What happens if we complete a notifiable acquisition without approval?
The acquisition is void under section 13 of the Act, so legal ownership does not pass as intended. Completing without approval is also a criminal offence, and the government can impose civil penalties of up to 5% of worldwide turnover or £10 million, whichever is greater. Individuals can face imprisonment on conviction. The acquirer should apply for retrospective validation promptly and take advice on the corporate and contractual consequences of the void transaction.
03How long does an NSIA review take?
After the ISU accepts a notification, the government has up to 30 working days to clear the acquisition or call it in. If called in, there is an initial assessment period of 30 working days, which can be extended by a further 45 working days and then by agreement with the acquirer. Information and attendance notices pause the clock during assessment. Acceptance itself can take some days, and incomplete forms are rejected, so preparation matters.
04Is a minority investment caught by the NSIA?
It can be. Moving from 25% or less to more than 25% of shares or voting rights is a trigger event, and in a mandatory sector it requires notification. Acquiring voting rights that enable the investor to pass or block resolutions is also a trigger. Material influence below those thresholds is not subject to mandatory notification, but the government can still call it in, and investors can notify voluntarily for certainty.
05Do internal group reorganisations need NSIA approval?
They can. The government's guidance states that an internal reorganisation can be a qualifying acquisition where a new entity in the group acquires control, even if the ultimate owner is unchanged. If the target carries on activities in a mandatory sector, the transfer may need notification and approval. The government has indicated it may exempt certain reorganisations in future, but until that change is made, intra-group transfers should be checked.
06What changes to the NSIA sectors were announced in 2026?
In its consultation response of 12 March 2026, the government confirmed it will add water as a new mandatory sector, create standalone schedules for critical minerals and semiconductors, narrow the artificial intelligence schedule to exclude routine use of off-the-shelf AI, and amend several other schedules, including data infrastructure. The changes require secondary legislation, so the current regulations apply until the new rules come into force. Deals in these areas should be checked against both sets of rules.
07Can we challenge an NSIA decision?
Decisions such as final orders can be challenged in the High Court by judicial review. Section 49 of the Act requires proceedings to be brought within 28 days, unless the court considers exceptional circumstances apply, so the decision to challenge must be taken quickly. In practice, many concerns are addressed by negotiating the terms of conditions during the assessment period, which is usually faster and more predictable than litigation.
Sources and official materials
- National Security and Investment Act 2021 — Call-in, mandatory notification, orders and offences
- NSIA guidance on acquisitions — Trigger events, timescales and the notification process
- The 17 types of notifiable acquisitions — Guidance on the mandatory sectors
- Guidance on compliance and enforcement — Penalties, offences and the government's approach
- Acquisitions outside the UK — How the Act applies to overseas entities and investors
- NSIA collection — Annual reports, consultations and final order notices
General information only, current as at 21 October 2026. It is not legal advice and does not create a solicitor–client relationship. It reflects the law of England and Wales unless stated otherwise; Scotland and Northern Ireland have separate legal systems, and the law changes frequently. Check current official sources and take advice on the facts of your matter.