MPs are calling for an inquiry into the role of the Crown Prosecution Service over the case of WikiLeaks founder Julian Assange.

A letter has been sent to the chairman of the Justice Select Committee saying evidence has come to light about the role of the CPS in relation to the inquiry by the Swedish authorities into allegations against Mr Assange.

The Australian-born journalist is being held in Belmarsh prison in London as he fights being extradited to the United States, with a crucial High Court decision due next week.

The UK’s National Union of Journalists and the International Federation of Journalists, amongst others, have highlighted the risks to journalism posed by this extradition

The letter says: “As you will know, for the last 14 years the Crown Prosecution Service has been the key public authority in the UK in the Julian Assange case, first in the extradition request concerning the Swedish case and now in the request for extradition to the United States.

“Julian Assange risks 175 years in prison for revealing classified documents that enabled the reporting of war crimes, torture and extrajudicial killings by drones.

“The UK’s National Union of Journalists and the International Federation of Journalists, amongst others, have highlighted the risks to journalism posed by this extradition, which would in their judgment criminalise common journalistic practices.

“The evidence that has come to light opens the CPS to allegations that it misjudged, or possibly overstepped, its role when advising the Swedish authorities on the extradition of Mr Assange to Sweden.

“This leads to questions about the motive behind such actions, including whether the CPS was influenced by another extradition request or aimed to facilitate Mr Assange’s subsequent extradition to the United States.”

The letter was signed by Labour MP John McDonnell, Conservative MP David Davis, Green MP Caroline Lucas and former Labour leader Jeremy Corbyn.