In defence of the realm – the National Security Act 2023 and the role of private investigators

According to Sir Ken McCallum, the incumbent Director-General of MI5, hostile foreign states were increasingly using proxies meaning the private security and intelligence sector to do their ‘dirty work’ for them (either knowingly or unwittingly), citing examples of alleged kidnap and blackmail, intimidation and manipulating public discourse.

In January 2025, the Home Office issued formal guidance in respect of the National Security Act 2023 to ‘Security Professionals’, namely private and corporate investigators and security professionals based or operating within the UK, seemingly in response to media coverage exposing the involvement of private investigators on behalf of hostile foreign states and entities.

The Act 

The Act came into force (at least in part) on 20 December 2023, repealing or updating parts of the old Official Secrets Acts of 1911, 1920 and 1939 (with the Official Secrets Act 1989 complimenting the new legislation). The term ‘national security’ throughout the Act has come to replace, and perhaps broaden, the original concept of ‘defence of the realm’.  The new Act encompasses not only counterterrorism but also security threats from other states, whether made directly or indirectly.

The Act made it possible for private investigators and intelligence professionals to be prosecuted and receive substantial custodial sentences if they carry out work on behalf of hostile foreign powers. It introduces a host of new offences, the most salient of which are, inter alia:

Espionage (Sections 1 to 3) is defined as ‘obtaining or disclosing information or trade secrets, without authorisation, and assisting a foreign intelligence service’, and carries a maximum custodial sentence of life imprisonment.

Sabotage (Section 12) introduces a new offence of sabotage conducted for, or intended to benefit, a foreign power, resulting in damage (including temporary damage) to any asset (tangible or intangible, including data and electronic systems) which is prejudicial to UK interests (the wide-ranging scope of this act will not be lost on the legal practitioner). It is intended as a bespoke, modern offence to tackle state sponsored sabotage conducted against the UK. The offence carries a maximum sentence of life imprisonment.

Foreign Interference (Section 13) creates a new offence of ‘foreign interference’ aimed at criminalising the disruptive activities of agents of foreign states, against the UK. The conduct of the accused must be (i) towards a specified goal (against the interests of the UK), must be illegitimate and must be carried out for or on behalf of a foreign power.  Again, the offence carries a maximum sentence of life imprisonment.

Obtaining a material benefit from a foreign intelligence service (Section 17) creates two new offences relating to obtaining material benefits from a foreign state’s intelligence service are also introduced in section 17 of the Act. The first offence concerns a situation where a person obtains, accepts or retains a material benefit, and they knew, or ought reasonably to know, that this benefit was provided by or on behalf of a foreign intelligence service. The second offence applies where a person agrees to accept (but does not receive) these material benefits. Where material benefits are obtained, the maximum sentence is 14 years’ imprisonment, compared to a maximum of 10 years’ imprisonment when such benefits are merely accepted. The purpose of this section is to allow prosecutions where a foreign intelligence service provides a person with financial or other less tangible benefits but the authorities are unable to prove a direct link between the benefit provided and the nature of that individual’s actual actions were (or were to be) in return. This provision effectively ‘fills the cracks’ where it would not be possible to meet a criminal threshold for the espionage offences listed above.   

Preparatory conduct (Section 18) is a new inchoate offence, committed when an individual engages in conduct deemed preparatory for the commission of certain offences under the Act, including those covering protected information, trade secrets, prohibited places or sabotage. Section 18 also applies to conduct intended to benefit a foreign state that involves serious violence, endangerment of life or serious risk to the public. Preparatory acts also apply if another individual commits the final act itself. This will be of significant interest to private investigators, who may conduct early or preliminary work for clients working for foreign, hostile states.

Guide to the National Security Act 2023 for security professionals

This Guidance was released in January 2025, almost certainly in response to a series of incidents where foreign states were linked to the sponsoring of kidnap, blackmail and illegal surveillance operations, conducted by private investigators. Its aim is to provide a steer to the new legislation for the private UK security sector.

The Guidance provides a clear and concise summary of state threat risks and assists in defining and providing contextualised meanings of the terms ‘dissidents’, ‘sensitive government, research of business information’ and ‘critical UK infrastructure’, as found in the legislation.

Perhaps of most interest in the Guidance is the reference to the Foreign Influence Registration Scheme (FIRS). FIRS compels both individuals and corporate entities to register certain arrangements carried out in the United Kingdom at the direction of a “foreign power” with the authorities, in a manner similar to the Foreign Agents Registration Act, which has been operational in the USA since 1938.

FIRS will require registration of any arrangement that authorises the carrying out of political influence activities in the UK at the direction of any foreign power (excluding the Republic of Ireland). There is also an enhanced tier that focusses on any arrangements carried out by certain foreign powers or entities specifically identified as posing a risk to UK safety or interests. The triggering conditions for such arrangements are defined as follows:

• Condition 1: an arrangement (whether formal or informal) with a “foreign power” (Political Influence Tier) or a specified foreign power or entity (Enhanced Tier);
• Condition 2: The arrangement involves a “direction” from the “foreign power” (Political Influence Tier) or a specified foreign power or entity (Enhanced Tier);
• Condition 3: The direction is to carry out “political influence activities” (Political Influence Tier) or “relevant activities” (Enhanced Tier), in the UK (whether by oneself, or with or through someone else); and
• Condition 4: There are no exemptions apply to the arrangement or activities (exemptions are detailed in the FRIS guidelines).

This now imposes a significant burden upon private investigators to self-regulate their activity with foreign entities or states. The direction of the legislation perhaps suggests the government is seeking to further regulate the security professional and private investigation sector. 

The future

The new Act and supporting Guidance represent the largest steps forward in espionage legislation since the Official Secrets Act of 1911. They implement fundamental amendments to the legal landscape of state security legislation and significantly empower prosecuting authorities with a wider scope of offences and investigatory tools with which to tackle espionage and related activity. 

Indeed, the Director General of MI5 has recently stated that his organisation now intends to prosecute espionage cases in the same manner as it currently prosecutes terrorism cases. This surely means that espionage and national security law is likely to be the new legal growth sector, as the scope of the new legislation will enable a greater range of conduct to be targeted. 

Lawyers themselves, particularly those involved in criminal law work, should undertake significant reviews of their practices and protocols in respect of instructions from foreign nationals that may have political links to hostile foreign states.

Additionally, those services that support law firms, especially in the fields of private intelligence and investigation work, should consider updating their compliance protocols, in particular with respect to foreign clients and clients with recognised security risk.  Additionally, the new offences of espionage introduced in the new law, covering the obtaining and/or disclosure of protected information and trade secrets, will no doubt require private investigators to be extremely mindful of the way their intelligence and data is collected, handled and processed, and to whom it is ultimately passed. 

Grosvenor Law frequently advises clients in respect of National Security and Official Secrets Act regulations and its compliance, both in relation to the civil and criminal legal spheres.