A court ruled last year that Mr Assange could be extradited despite claims he is a suicide risk and that handing him over to the US would breach his human rights.

Dunja Mijatovic, the Council of Europe commissioner for human rights, has now written to Ms Patel, calling on her not to extradite Mr Assange because of the “wider human rights implications”.

Mr Assange is wanted over allegations of a conspiracy to obtain and release national defence information following the publication by Wikileaks of hundreds of thousands of leaked documents relating to the wars in Afghanistan and Iraq.

Ms Mijatovic said: “It is my view that the indictment by the United States against Mr Assange raises important questions about the protection of those that publish classified information in the public interest, including information that exposes human rights violations.

“The broad and vague nature of the allegations against Mr Assange, and of the offences listed in the indictment, are troubling as many of them concern activities at the core of investigative journalism in Europe and beyond.

“Consequently, allowing Mr Assange’s extradition on this basis would have a chilling effect on media freedom, and could ultimately hamper the press in performing its task as purveyor of information and public watchdog in democratic societies.”

She added that “the government of the United Kingdom should not allow his extradition to the United States”.