One of Boris Johnson's senior advisers has quit after apparently remarking that Caribbean immigrants should go home if they did not like London.
The Mayor of the capital insisted that James McGrath, who was influential in getting him elected to City Hall last month, was not a racist.
But Mr Johnson said Mr McGrath, his political adviser, would only provide "ammunition" to the Tory mayor's critics if he was to remain in post.
Mr Johnson accepted the resignation of Mr McGrath after an interview with the adviser appeared on the internet on Sunday.
In it he was challenged with the suggestion by prominent black commentator Darcus Howe that Mr Johnson's election could cause an exodus of Caribbean immigrants to their homelands.
In response, Mr McGrath was quoted as saying: "Well, let them go if they don't like it here."
The Mayor said Mr McGrath had been quoted "out of context" by Marc 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.
"London is blessed with a rich ethnic and cultural diversity. It is one of the main reasons why I regard it as the greatest city on earth, and I am determined, as Mayor, to serve each and every community with equal passion and commitment."
