Columnists give a newspaper its edge and flavour, its zest and colour. They are often outspoken, always provocative and can usually be relied upon to spark a furious response. They should be allowed to campaign fearlessly for what they believe to be right, but as CP Scott wrote: "The voice of opponents no less than that of friends has a right to be heard. Comment also is justly subject to a self-imposed restraint. It is well to be frank; it is even better to be fair."

These words came to mind when reading a letter from several co-signatories who felt that Observer columnist Nick Cohen had gone beyond the bounds of reasonable comment when he asked Shiraz Maher, the co-author of a paper on the government's counterterrorism strategy, why he had not offered it to left think-tanks such as the Fabians or the Institute for Public Policy Research. Cohen reported that Maher had guffawed at the suggestion. "They would never print what he wrote. For this Muslim liberal, the left was no longer a home but an obstacle."

Fabian general-secretary Sunder Katwala saw this as a direct accusation that his and other left organisations had deliberately suppressed criticism of Islamist extremism. He launched a furious denial on his blog which met an equally spirited blog from Cohen, in which he admitted to sharing Maher's "contempt" for the Fabians.

Then former New Statesman political editor Martin Bright joined in, accusing Katwala of bullying Cohen and trying to silence him.

It's tempting to dismiss all this as just so much scrapping by a small clique, but let's look a little closer at the detail. Shiraz Maher, Cohen's "Muslim liberal", is a former Islamist activist who associated with Glasgow bomber Bilal Abdulla, recently jailed for at least 32 years. Readers should have been told that.

Maher wrote in the Mail on Sunday last month about government ministers being unwilling to promote the idea of Britishness, yet the concept of what it is to be British is central to Gordon Brown's government and has been a major Fabian theme. If Maher really is this out of touch with democratic public debate, it calls into question his credibility on the subject of think-tanks.

Katwala told me that Maher had never had any contact with the Fabians or the IPPR, but "his co-authored paper is quite good; it contains nothing we could not have published", so it would appear that Maher and Cohen's accusation of censorship is without foundation in this case.

As a footnote, I offer the unrelated story of Hassan Butt. He claimed to be a former al-Qaida operative who called upon his fellow Muslims to renounce violence. He wrote a piece for the Observer in July 2007 which readers praised for its bravery; Nick Cohen, along with many others, wrote about him last year.

However, at a recent trial of another man accused of terrorist offences, Butt said that he had made the whole thing up, telling journalists stories "the media wanted to hear" and admitting that he was "a professional liar".

• Stephen Pritchard is president of the Organisation of News Ombudsmen

reader@observer.co.uk