Ken Livingstone has pledged to stand down as Mayor if he breaks his word on putting up the congestion charge.

He told millions of BBC Newsnight viewers he would not increase the £8 charge for ordinary cars if re-elected.

By promising to resign over the issue Mr Livingstone has made trust a central issue of his campaign.

There has been concern over his probity ratings after a recent opinion poll showed Londoners considered him the least honest of the main candidates.

"I'll give you this guarantee," Mr Livingstone said during the live television debate against Tory Boris Johnson and Lib-Dem Brian Paddick last night.

"If I break my word and increase the congestion charge for cars below the polluting level, I will resign."

Mr Paddick asked: "How do voters know that the promises you make today, when you get back in office, you won't change your mind again?"

But the Mayor replied: "I've given an absolute commitment just now. I will not break my word. If I did, I would step down from the job. I would guarantee that ordinary cars stay at £8. We only want to get the gas-guzzlers off the streets."

He brushed off remarks by presenter Jeremy Paxman that in 2003 he had said he could see "no circumstances" in which the C-charge would be increased from £5 but had put it up two years later. He also came under pressure for promising to serve only one term as Mayor and then changing his mind.

Mr Paddick attracted the scorn of the "attack dog" presenter when he refused to divulge which of his rivals would get his second preference endorsement. His decision could determine the outcomeof the mayoral race as the Lib-Dem candidate has hundreds of thousands of supporters.

"I think Londoners are between a rock and a hard place looking at these two candidates to my left," he said. "I haven't made my mind up yet, it's a very difficult decision. I think they are bad in different ways." However, Mr Livingstone said he would "without a moment's hesitation" back Mr Paddick if he hadn't already endorsed Green candidate Si‚n Berry.

Tory candidate Boris Johnson also came under pressure from Paxman who quizzed him over the costings for his new generation of Routemasters. Mr Johnson has said it would cost just £8 million a year to replace bendy buses with the new fleet, figures that have been hotly disputed by Labour.

Last night, he admitted it would cost nearer £25 million to provide the buses with conductors but refused to be drawn on the cost of building them.

Despite repeated calls of "Give us a figure!" from his mayoral rivals and Paxman he would say only that they would cost "no more and no less" than Mr Livingstone's plans for 500 new hybrid buses.

The Tory MP was criticised by rivals for his lack of experience in running a big organisation. The Mayor's City Hall empire employs around 105,000 people while Mr Paddick was responsible for thousands of officers during his time at the Metropolitan Police.

Mr Johnson hit back: "I have run an extremely effective private sector organisation [as editor of The Spectator magazine] and indeed I'm the only candidate at this election with any experience of holding down costs in the private sector."

Teased by Mr Paddick for boasting he had been responsible for 50 people, Mr Johnson said: "Your viewers will be interested in the way the Liberal candidate scorns organisations. They are the backbone of the economy and they are what we should be supporting."

WE WERE ALREADY DEALING WITH JASPER, CLAIMS LIVINGSTONE

ORGANISATIONS linked to former mayoral aide Lee Jasper were being investigated before an Evening Standard exposÈ, Ken Livingstone has claimed.

The Mayor's remarks on a Newsnight debate last night were apparently at odds with the actual course of events.

The Standard first revealed that his former race relations adviser was at the centre of a network of companies which had received City Hall funds in December but appeared to do little or no work in return.

On 5 December, Mr Livingstone said the Standard's revelations were a "tissue of lies" which would not be investigated.

He told BBC London: "There is not the slightest question ... of my dealing with [the Standard's enquiries.] I'm not interested in anything Andrew Gilligan throws up. The man has been a consistent liar." Asked how he knew the stories were "lies" if he refused to investigate them, the Mayor replied: "For all the projects, there's a full audit trail, with chapter and verse on how the money's been spent." Days later Mr Livingstone announced an internal inquiry but it was not until January this year that a full police investigation was launched. Hundreds of thousands of pounds of public money was unaccounted for.

Mr Jasper quit last month over a string of sexually-charged emails to a woman involved in running one of the projects.

Last night, Newsnight presenter Jeremy Paxman asked the Mayor: "The LDA, seven organisations that are funded by that, are currently being investigated by the police."

Mr Livingstone said: "Out of the thousands they have funded over eight years, we have found seven where either the money has been misappropriated...

"They were all being investigated long before the Evening Standard got onto it."

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