British police forces could find it easier to access journalists’ private emails as a result of legislation making its way through parliament, according to freedom of speech campaigners, who are urging politicians to make a last-minute intervention to secure journalistic freedom.

Michelle Stanistreet, the general secretary of the NUJ, said the crime (overseas production orders) bill, due to be debated in the Commons on Wednesday, also “paves the way for the Home Office to surrender up the content of our electronic communications to foreign governments”.

The legislation is designed to make it easier for British authorities to access data stored overseas by foreign technology companies such as Facebook and Google, which can currently take months to obtain, while also enabling greater sharing of UK-based data with foreign governments.

However, campaigners fear the law could sidestep existing protections on what data can be accessed by the British authorities. Many news organisations and individuals rely on email and social media services provided by US companies, which means their data is often held overseas.

Rebecca Vincent of Reporters Without Borders said: “The fact that this bill is incredibly technical and complex is perhaps why it has largely evaded public scrutiny for so long, but the implications are potentially very damaging to press freedom and broader human rights.

“Against a backdrop of other recent moves that will serve to restrict press freedom in the UK, such as the counter-terrorism and border security bill, which will likely be adopted any day now, this is very worrying indeed. The bill merits intervention even at this late stage of debate.”

A Home Office spokesperson said “no one should be above the law” but insisted journalists’ concerns had been listened to.

Groups including Reporters Without Borders, Index on Censorship, English PEN, Big Brother Watch and the Open Rights Group have signed a public letter warning that many of the powers in the bill are unprecedented and could overrule existing safeguards in British law.

The letter also raises concerns that the legislation could make it easier for foreign governments with weak press freedom to request data held in Britain. Campaigners say such provisions could be used by countries to monitor exiled journalists based in the UK.

The letter urges MPs and peers to ensure existing protections for freedom of expression and privacy rights are built into the new legislation.

The Home Office said: “The tools available to our law enforcement must be fit for the online world in which we live. Ninety-nine per cent of data linked to child abuse is held overseas and the faster we get it the quicker we can stop abusers.

“This legislation, where an international data access agreement is in place, would give police and prosecutors quicker and easier access to vital electronic data held outside the UK.

“We have listened to concerns and made sure that journalists will be informed in advance of an application being made to the court. This will give them the opportunity to make representations to the judge at the time of the application.

“No one should be above the law but we have recognised journalists’ concerns by tabling a range of amendments.”