The London Review of Books has posted a public apology on its website after some of Britain's most distinguished writers, academics and arts figures accused the magazine of publishing a racist blogpost comparing African migrants to baboons and black shopkeepers to rottweilers.

The apology represented a significant climbdown for Britain's revered literary magazine, which had originally summarily dismissed the complaints and refused to publish a letter signed by more than 70 leading cultural figures.

The letter, whose signatories included award-winning writer, Caryl Phillips, poet Michael Rosen, playwright and broadcaster Kwame Kwei-Armah and London School of Economics professor Paul Gilroy, expressed astonishment that the magazine had published an "egregious" blog by RW Johnson on July 6th.

The LRB received several similar criticisms about the piece but 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 posting from the website 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."

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."

By late afternoon the magazine retreated further, publishing the following apology: "We have had a number of complaints about a post on the LRB blog on 6 July on the grounds that it was racist. The LRB does not condone racism, nor does the author of the post, RW Johnson. We recognise that the post was susceptible of that interpretation and that it was therefore an error of judgment on our part to publish it. We're sorry. We have since taken the post down."

Johnson said he had not been told the piece had been taken down and rejected accusations of racism.

"I've only just arrived back from a trip in a game reserve and have no knowledge of this. I would be astonished at any allegations of racism," he wrote in an email.

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".

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".

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.