Index on Censorship has defended its decision to establish formal links with the comedian Steve Coogan after two high-profile patrons stepped down from the freedom of speech group over the appointment.

The Private Eye editor Ian Hislop and his deputy Francis Wheen resigned in protest at the decision of the charity to accept Mr Coogan, a high-profile campaigner for the press regulation reform group Hacked Off, as one of its patrons.

Mr Wheen, a leading journalist and broadcaster, said he was stepping down because he believed Mr Coogan did not have a long-standing record on freedom of speech issues and was principally allied with Hacked Off which, he said, “most journalists regard as an enemy of the free press”.

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Mr Hislop declined to comment. But the decision of the two most senior figures at Britain’s most redoubtable satirical magazine to step down over Mr Coogan’s appointment will be embarrassing for Index on Censorship, which was founded in 1972 with the backing of poet Stephen Spender to give voice to the stories of dissidents behind the Iron Curtain.

Jodie Ginsberg, the charity’s chief executive, insisted there was no conflict between its values and the appointment of Mr Coogan.

She added that it remained opposed to the cross-party Royal Charter on press regulation, which arose from the Leveson Inquiry findings and is strongly supported by Mr Coogan and Hacked Off.

The international campaign group pointed out that at least one other of its patrons, the playwright Sir Tom Stoppard, also supported the Royal Charter. Michael Palin, another patron, was one of 200 signatories from the arts and academia to a letter declaring support for the system.

Newspaper and magazine groups have declared their intention to regulate themselves outside the Royal Charter, which they criticise as a form of state intervention in the freedom of the press.

Ms Ginsberg said: “Free speech depends on open debate with people who may have points of view you disagree with. We regret that Ian and Francis have chosen to resign from our wide group of patrons. We have made it clear from the outset that we will not be changing our position on the Royal Charter.”

When it was announced last week that Mr Coogan was joining Index on Censorship, the comedian said he was joining to fight for “creative and artistic freedom of expression”. He said: “I am pleased to lend my support and patronage to such an important cause.”

But critics said they saw Mr Coogan’s new role as incompatible with his funding and support of Hacked Off .

Mr Wheen told the Daily Mail: “His appointment is a slap in the face. Some of the other patrons want Leveson’s recommendations to be implemented but the point about Stoppard is that least he does have a long and honourable record of defending freedom of expression elsewhere.

“Whereas Coogan by his own admission, as far as I can see, has never been involved in any such defence of free expression or anything even remotely connected with freedom of speech or the press except for being involved in Hacked Off.”

Evan Harris, campaigns director of Hacked Off, said: “There is absolutely no conflict between support for Leveson and supporting freedom of expression. A Leveson-style regulator is the opposite to a threat to freedom of expression. A false distinction is being drawn here.”