Mayor's aide quits in racism row after saying Caribbean immigrants should go home if they didn't like life under Boris

James McGrath was reported to have said 'let people go if they don't like it here' in response to a suggestion that Caribbean migrants might return to their homelands after Mr Johnson had become London mayor.

The remarks by the mayor's deputy chief of staff were disclosed yesterday by black rights campaigner and Labour activist Marc Wadsworth.

They were made in a meeting between the two last month.

'James is not a racist': Mayor Boris Johnson (right) has defended  former polititcal advisor James McGrath who was forced to stand down

Mr Wadsworth had pointed to a claim by commentator Darcus Howe that the election of 'Boris Johnson, a right-wing Conservative, might just trigger off a mass exodus of older Caribbean migrants back to our homelands'.

Mr Wadsworth claimed on his internet blog: 'He retorted: "Well, let them go if they don't like it here".'

He said the remarks showed Mr McGrath, an Australian, was 'far from the politically correct, David-Cameron-new-cuddly-Conservative Party'.

'His comments about black people are robust and as distant from being politically correct as his country,' he added.

Mr Wadsworth also said Mr McGrath had called him 'sunshine', which he claimed was 'not a politically correct thing to say to a black person'.

In a bid to draw a line under the controversy, Mr Johnson moved swiftly to discipline his political adviser.

The mayor said he had accepted Mr McGrath's resignation, saying he would only provide 'ammunition' to the Tory mayor's critics if he was to remain in post.

But Mr Johnson insisted his aide, who was influential in getting him elected to City Hall last month, was not a racist.

Mr McGrath had earlier hit back in a letter to Mr Wadsworth strongly refuting any charge of racism.

'As an immigrant myself I would wish to assure you that I would not want anyone to feel because of their background that they felt the need to leave this fantastic city or the UK,' he said.

'Indeed, if I recall my comment was in response to you raising inflammatory comments made during the election campaign by an openly Ken Livingstone-supporting columnist.

'The columnist suggested that older people from the Caribbean might migrate back to their homelands if Boris Johnson became Mayor.

'I felt that this suggestion was ridiculous and intended as a slur and responded by saying with words to effect of "let people go if they don't like it here".

'To imply that I meant that all black people who didn't support Boris Johnson should leave the country is utterly absurd and incorrect.'

However, Mr Johnson said both he and Mr McGrath had subsequently 'agreed' he could not stay on as his political adviser.

The Mayor said Mr McGrath had been quoted 'out of context' by Mr Wadsworth, a so-called citizen journalist, but the remarks made it impossible for him to continue in his role.

'James is not a racist. I know that,' Mr Johnson said.

'He shares my passionate belief that racism is vile, repulsive and has no place in modern Britain.

'But his response to a silly and hostile suggestion put to him by Marc Wadsworth, allowed doubts to be raised about that commitment.

'James's remark was taken out of context and distorted, but he recognises the need for crystal clarity on a vital issue like this.

'We both agree that he could not stay on as my political adviser without providing ammunition for those who wish to deliberately misrepresent our clear and unambiguous opposition to any racist tendencies.'

Mr McGrath, a 34-year-old Australian, was appointed director of political strategy at City Hall following Mr Johnson's narrow victory over Ken Livingstone last month.

Shadow cabinet minister Francis Maude hailed him recently as 'one of our real big hitters', crediting him with helping the turning around the Tories nationally.

He has worked for the Conservative Party for seven years.

Influential Tory blogger Iain Dale criticised the Mayor for letting Mr McGrath go.

'James McGrath is a no-nonsense Aussie,' he wrote. 'He doesn't beat about the bush, but these remarks could have been made about any group who 'don't like it here' - white, black, whatever.'

Mr Dale added: 'What he should have done is stand by the man who has stood by him through thick and thin over the last eight months.

'What he has done today is create a rod for his own back.'

 • Last year, David Cameron sacked Tory front-bencher Patrick Mercer, over controversial remarks he made about the treatment of minorities within the Armed Forces.

Patrick Mercer, a decorated colonel who saw service in Bosnia and Ulster, sparked controversy after saying many ethnic minority soldiers were 'idle and useless' and that they used racism as an excuse for their shortcomings.

He said it was commonplace for troops to be given a hard time over their ethnicity, the colour of their hair, or because they were overweight, describing how black troopers were routinely called 'black bastard' in the forces.

He added: 'But that's the way it is in the Army.'