One of Boris Johnson’s most senior advisers was forced to resign last night after he plunged the Mayor of London into another racial controversy, saying that immigrant blacks could leave if they did not like the Tory administration.

Mr Johnson initially defended James McGrath, his senior political strategist, but last night sought his resignation, saying that the remarks would further damage his reputation on race issues. The mayor said that Mr McGrath’s comments were taken out of context, but he could not continue to work for him because it would “provide ammunition” for his opponents.

The furore came after Mr Johnson raised the hackles of equality campaigners last week for dropping the central anti-racism message of the Rise festival. He has been criticised in the past for calling black children “piccaninnies” and saying that black people had “water melon smiles”.

In the latest controversy Mr McGrath made the remarks when questioned about the suggestion that Mr Johnson’s win could result in the departure of many older Caribbean immigrants from the capital. According to Marc Wadsworth, the anti-racism campaigner writing on the internet news site www.the-latest.com, Mr McGrath replied: “Well, let them go if they don’t like it here.”

Late yesterday afternoon there was no indication that Mr McGrath’s position was under threat. However, Mr Johnson’s action, a few hours later, highlights the mayor’s sensitivity over race. The Times understands that he was also motivated in part by an intention to show distinct differences between his administration and that of his predecessor, Ken Livingstone.

Mr Johnson said last night that there was a need for “crystal clarity” on the issue of race. “James is not a racist. 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,” he said.

Mr Wadsworth said that he was shocked by Mr Johnson’s swift reaction as he “didn’t want to make a big fuss”. However, he said it was the right decision as the remarks were “insensitive at the very least”.

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