'End London's Punch and Judy politics'

Lord O'Donnell, who stepped down as Cabinet Secretary last year, said Londoners deserved "a better choice", as he attended the campaign launch of "mother for mayor" candidate Siobhan Benita.

Ms Benita, 40, worked in the heart of British government for 15 years but left Whitehall in January to run for Mayor. Today she described Mr Johnson and Mr Livingstone as "anti-role models" and said their campaigns had become "ridiculous".

Gus O'Donnell- known in Whitehall as "God" - said the Mayor should not be "constrained by party politics" and independent candidates would "add a new dimension".

He added: "I'm a big fan of the idea of there being greater choice in mayoral elections. As a crossbencher in the House of Lords you can see the value independents can bring to legislature.

An independent can just say what is in the best interests of London.

"Because of the dominance of party politics ... it's the Boris and Ken show. I hope we can have a better choice."

Lord O'Donnell said he wanted to see independents run for mayor across Britain: "It would be good for a lot of people fed up with party politics and ... Punch and Judy politics".

Ms Benita, from New Malden, is a former senior official at the Cabinet Office. She said: "The way Boris and Ken are acting, they've become anti-role models. With two daughters of my own, I frankly don't want them seeing that. I'm getting increasingly angry at both of them. London deserves better."

At last night's event, held at the offices of Ernst & Young, she launched a range of policies, including free travel for Londoners who are actively seeking work and reduced fares for people on the minimum wage.

She said she would appoint a Young Mayor of London who would have a say on all policy areas, and would set up a Youth Assembly to ensure the concerns of young Londoners were at the heart of her administration.

Ms Benita added: "The big thing I want to stress is that an independent Mayor is better for London. During the campaign so far, it's like Ken and Boris have been playing poker.

"It's ridiculous. They are making all these promises and I don't believe any of it any more - I don't think the public believes it either. I don't want a big idea like a new Routemaster or a promise I can't deliver. Harnessing the potential of Londoners would transform this city. My big idea is people."

She said Lord O'Donnell, who worked with prime ministers John Major, Tony Blair and Gordon Brown, was offering her advice and support on her policies: "Gus is a supporter and an advocate. If Gus doesn't know the answer he knows a man who does."