The London Review of Books has rebuffed some of Britain's most distinguished writers, academics and arts figures who accused the magazine of posting a racist blogpost comparing African migrants to baboons and black shopkeepers to rottweilers.

Seventy-three cultural figures including award-winning writer, Caryl Phillips, poet Michael Rosen, playwright and broadcaster Kwame Kwei-Armah and London School of Economics professor Paul Gilroy, signed a letter expressing their astonishment that the magazine's blog had published an "egregious" post by RW Johnson on July 6.

The piece, "After the World Cup", started with the line: "We are being besieged by baboons again," before going on to describe how the apes scavenge for food and had seen off a local rottweiler that attacked them. In the next paragraph Johnson referred to African migrants, writing: "they too are here essentially searching for food". He went on to relate how several dozen of the migrants had been murdered at the instigation of "local black shopkeepers".

Editor Mary Kay-Wilmers refused to publish the letter, claiming the signatories had imagined an "explicit connection" between baboons and migrants that did not exist. LRB insiders say several staff had tried to persuade Wilmers to remove the posting in the previous week to little avail. In a brief reply she explained that to publish the letter would be effectively introducing a racial slur and she was not "willing to be the cause of its appearing in print".

By the time she had received the letter she had, however, already removed Johnson's post from the site after it had been up for 13 days, arguing: "We should have realised in the first place that it was possible to read the post in the way that you read it. Had we done so, we would certainly not have published it."

The letter argued: "Whilst it might be unfair to pick on a man for his inability to be funny, we believe that it would be wholly wrong to stay silent when he resorts to peddling highly offensive, age-old racist stereotypes that the LRB editorial team deems fit to publish". It was also deeply critical of the magazine's continued use of Johnson, whose work they claim is "often stacked with the superficial and the racist".

Last night, many of the signatories expressed their disappointment in Wilmers's response, describing it as "disingenuous" and "in denial". "There's nothing subtle about the piece," said Phillips, who is a professor at Yale University. "And this was the version that had been edited. The idea that there's a reading of it that the LRB just missed is preposterous. If you put that in front of undergraduate students every single one of them would understand what it meant."

Poet and blogger Katy Evans-Bush mocked the idea that an organ renowned for its complex appreciation of erudite work could claim to have missed the connection: "She's being extremely literal for someone who edits on of the most sophisticated literary publications in the world."

Michael Rosen described her letter as "classic low cunning". "She's a very sophisticated literary woman. She understands the power of juxtaposition so she must be in denial."

The former director of literature at the Arts Council and current principal at Cumberland Lodge, Alastair Niven, said the LRB "should have the bigness to admit it's made a mistake" and that if it fails to do so the Arts Council should rethink its funding.

This morning Wilmers softened her position, accepting that an explicit connection could be made: "We didn't read it carefully enough, we didn't see it, we didn't imagine it." She did, however, mount a staunch defence of Johnson, saying, "The LRB is not racist. He's not a racist but he's not always aware of how he comes across. He went back to South Africa and has done a lot of brave work in Zimbabwe with the MDC." Asked if her reply was her last word to the signatories she said: "I'm quite sure we haven't discussed it enough."

Mr Johnson was not available for comment.