Britain’s “antiquated” Official Secrets Act needs to be updated by introducing a public interest defence as well as longer prison sentences to punish those who betray sensitive information, the official body that advises the government has said.

Proposals by the Law Commission to change the legislation that governs public servants include removing the need to prove any leak “caused damage” and replacing the word “enemy” with “foreign power” so as to include terrorist organisations and companies controlled by another state.

The recommendations from the official body that advises the government on revising legislation and creating an Espionage Act have been released to coincide with the return of parliament.

The recommendations are not binding but have been developed, in close consultation with government, from work originally commissioned by the Cabinet Office in 2015.

“New communications and data technology has changed the nature of espionage and leaks,” the commission’s 12-page summary of the report notes.

“For example, hostile states can conduct cyber-attacks on the UK through multiple servers across multiple countries. At the same time, the potential impact of spying and leaks has increased: a single disclosure could contain terabytes of data.”

The Russia report, published by parliament’s intelligence and security committee in July, “highlighted the need for reform of the 1911 Official Secrets Act to ensure that espionage can be properly prosecuted”, the report adds.

Prof Penney Lewis, the commissioner for criminal law on the Law Commission, said: “In the last 20 years, the world has moved on but these vital laws protecting our national security have not kept up. They are in urgent need of reform.

“Our recommendations will help to give the government the tools it needs to respond to espionage and leaks, whilst also being proportionate and protecting individuals’ human rights.”

Publication of the commission’s original consultation proposals in 2017 provoked controversy when it suggested increasing prison terms from two to 14 years and did not include safeguards for whistleblowers or journalists.

In its final recommendations, the commission suggests longer, maximum prison terms are required to deter and punish the most serious cases of espionage but it “does not make a recommendation on what new maximum sentences should be”.

One of its main proposals is that: “A statutory public interest defence should be available for anyone – including civilians and journalists – charged with an unauthorised disclosure offence under the Official Secrets Act 1989. If it is found that the disclosure was in the public interest, the defendant would not be guilty of the offence.”

To meet that requirement, it proposes, “both the subject matter being disclosed” and “the manner of disclosure” would have to be in the public interest.

Public servants and civilians should be enabled to report “concerns of wrongdoing” to an independent statutory commissioner who would be tasked with investigating such complaints.

The report calls for the requirement to prove that any leak caused damage be removed in prosecutions of crown servants and contractors who leak information.

“Instead,” it says, “the offence should require proof of a sufficiently culpable mental state (which should be decided by parliament). For example, knowledge or belief that the disclosure would cause damage.”

Under the Official Secrets Act as it exists now, anyone who is not a British national or a public servant does not commit an offence if they engage in espionage against the UK while abroad.

That is too restrictive, the report notes. The offences should be expanded so that they can be committed irrespective of an individual’s nationality.