Boris Johnson said London needs more police officers on the beat

The Conservative mayoral candidate said financial institutions in the City of London should give more money to voluntary groups tackling the problem.

Plans to create a "Mayor's Fund" for the financial sector were at an advanced stage, said Mr Johnson.

He said more details would be revealed closer to the election on 1 May.

'Flim flam'

"I want to encourage people who are benefiting from London, the world's financial capital, who make colossal sums, to show more awareness of their debt to this city and to give more to those groups," he said.

Some banks were already beginning to show more generosity but the mayor's office must do "much, much more", he added.

My plan is to change the way we fund the voluntary sector by making all grants cover at least three years Sian Berry, Green Party mayoral candidate

But Mr Livingstone's campaign team said Mr Johnson's scheme would raise small sums compared to the �78m the mayor has committed to youth services across London.

A campaign spokesman said: "This is typical flim flam from Boris Johnson's campaign to cover up the legacy of the Tories in slashing youth services in London."

Lib Dem mayoral candidate Brian Paddick insisted a proper financial audit of City Hall was needed "before asking any businesses for money, otherwise it will just be a case of throwing good after bad".

The Green Party attacked the pledge as "headline grabbing" and insisted that relying on voluntary contributions from the City to solve London's social problems was unsustainable.

"My plan is to change the way we fund the voluntary sector by making all grants cover at least three years," said the party's mayoral candidate Sian Berry.