Lee Jasper resigned on Tuesday Lee Jasper's career

Lee Jasper, the mayor's former chief race adviser, blamed what he called a racist media campaign for his decision.

Mr Jasper had been at the centre of allegations over the misuse of public funds and was due before the London Assembly on the matter on Wednesday.

After stepping down on Tuesday he said he wanted a "categoric investigation" into the claims.

The resignation comes after the Evening Standard newspaper published claims that Mr Jasper had sent intimate e-mails to a woman involved with organisations which received money from City Hall.

Directly responsible

Other allegations made by the newspaper concern money paid by the London Development Agency (LDA), the mayor's business arm, to a number of black organisations.

Mr Jasper said: "They (the London Development Agency) had 10 weeks to ask me a question - they didn't.

"I referred the matters to the police. I want a categoric investigation and hopefully that's what will occur."

Mr Jasper had been due to face the London Assembly to answer questions about his involvement in the community projects which received funding from the mayor's office.

Tory mayoral candidate Boris Johnson has called for the mayor to take Mr Jasper's place at the meeting.

Mr Johnson said: "He (Mr Livingstone) has repeatedly said he is directly responsible for the actions of his advisers and he should take Jasper's place and answer the questions that Jasper won't."

And Liberal Democrat mayoral candidate Brian Paddick said the "resignation raises serious questions about the mayor's judgment".

Disgraceful campaign

An internal inquiry in January cleared Mr Jasper of any wrongdoing but he was suspended by the mayor, pending a police investigation.

At a question and answer session on Tuesday evening the mayor criticised the Evening Standard.

"I think it has been an absolutely disgraceful campaign," he said.

He also said he would "bet my own life" that a police investigation would clear Mr Jasper, "and I will reappoint him when they do".

During prime minister's questions, Gordon Brown said the allegations should be investigated by the police, while Tory leader David Cameron said the alleged activities were "completely unacceptable".

It was never a question of racism Evening standard statement

The Metropolitan Police is investigating six allegations of fraud in connection with six organisations that received public funding.

But it said allegations of misconduct, where there was no evidence of a crime, were not a matter for the police.

In his resignation letter to the mayor, Mr Jasper said: "It has become clear that a number of matters which are not of first importance in London are being used to distract from the crucial questions in the election campaign.

"The racist nature of a relentless media campaign and the consequent effects on myself and family have placed an intolerable strain on all of us."

A statement from the Evening Standard said its investigations had been about "demanding transparency on the spending of public money".

"It was never a question of racism," it added.