"[2] The core measures put in place by the act came into force on 20 December 2023 and were described at the time as "the most significant reform of espionage law in a century".

The offence of obtaining or disclosing protected information replaces provisions in prior Official Secrets Acts, and increases the maximum sentence to life imprisonment from 14 years previously.

The Ministry of Defence stated that former UK Armed Forces personnel training foreign militaries was an example of conduct which could involve "disclosing protected information"[6] and would therefore constitute an offence under this section.

[7] An example is given of "a person taking photographs of staff members as they enter or leave a prohibited place would commit the offence if they did so with a purpose that they knew, or ought reasonably to know, is prejudicial to the safety or interests of the United Kingdom".

Three conditions which must all be met in order for the prosecution to be successful are:[13] Activities "carried out for, or on behalf of, or intended to benefit, a foreign power" fall under this rubric.

Foreign interference "is intended to sow discord, manipulate public discourse, discredit the political system, bias the development of policy, and undermine the safety or interests of the UK."

A Home Office policy paper describes a military contractor with security clearance researching foreign diplomats in London, with the intention of sharing sensitive information in exchange for money, as a hypothetical example of a preparatory conduct offence.

[18] Section 56 provides for an offence which is committed when an individual subject to a STPIM contravenes (without reasonable excuse) any measure specified in the notice.

For breaching a measure preventing travel outside the United Kingdom a sentence of 10 years imprisonment can be imposed and the grounds of reasonable excuse are excluded.

This section makes provision for powers of entry, search, seizure and retention in relation to individuals subject to a STPIM.

Guy Black, deputy chair of Telegraph newspapers, told the House of Lords that he was concerned the draft legislation could “potentially criminalise” reporters and whistleblowers.

[20] An amendment in the Lords to address journalistic concerns by adding "a defence to show that the person engaged in the conduct in question was acting with a view to publication of material by a recognised news publisher" was defeated by a majority of 130 votes.

[22] The act has been criticised in Chinese media outlets, which claimed that it was comparable to or stricter than the Hong Kong national security law.