Labour will be looking to Mr Livingstone to salvage something from a night that saw them slump to third place in the national vote share.

The election will also decide the 25 members of the London Assembly, which scrutinises the work of the mayor.

Vote counting begins at 0830 BST and is expected to take up to 12 hours.

The process will take place at three venues - Alexandra Palace, Excel and Olympia - and the new mayor will be declared at City Hall on Friday evening.

Labour -- with Brown leading them into elections for the first time since taking office last year -- is set to finish third behind the opposition Conservatives and Liberal Democrats, the BBC said.

The ruling party could face further humiliation in the tightly-fought London mayoral race, which pitched the current mayor, Labour's Ken Livingstone, against the Conservatives' maverick Boris Johnson.

Amid growing speculation Livingstone would be voted out as part of the backlash, Brown said he spoke to him last night and thanked him "for the campaign he has run and the message he has put across."

As the vote count continued -- the London result was not due until after 1600 GMT -- the BBC reported that Johnson was ahead, while betting firm Paddy Power said it was paying out on a Johnson win even before the result was known.

"After the kick in the ballots that Labour has had overnight, we expect Boris to put the final nail in their local elections coffin," said a spokesman for the firm.

Brown has been shaken in recent months by poor opinion polls and by lawmakers' dissent over tax reforms and plans to extend the period of pre-trial detention for terrorist suspects to 42 days.

It seems unlikely that he will face a leadership challenge in the wake of the results, but most commentators expect him to try and relaunch his government with a new policy programme.

While a Johnson victory would be another huge boost for the Conservatives, a Livingstone win could reassure Labour that their dip in form is only temporary.

Outside London there are several progressive candidates standing, for a variety of parties and we wish them all well.

 In London, vote for Ken Livingstone for Mayor; and George Galloway for the GLA (Respect - 11th on the orange ballot paper)

In City and East constituency in London, vote Hanif Abdulmuhit (Respect - number 1 on the yellow ballot paper)

RESPECT
As Salma Yaqoob has written

“The broad constituency in favour of peace, equality and social justice is growing. On many issues it is even a majority in society. Millions of people are against war, against privatising and running down the welfare state, against racism, and for greater equality. There is an opportunity to be a voice for these millions, and to offer an electoral alternative to the parties of war and injustice.

“The challenge for Respect is to be able to work with, and be a voice for, this growing broad progressive constituency. This constituency includes people who remain tied to Labour or other parties such as the Greens. We have to work patiently to build up our vote at a local level. But we also have to be part (and almost certainly a minority part) of a much wider network of alliances.”

At a strategic level, Respect has positioned itself very well in the London elections, as the most left wing part of the politically relevant mainstream, and part of a broadly progressive alliance to ensure the re-election of Ken Livingstone, that includes the Green Party, trade unions, as well as BME and faith groups; while at the same time campaigning that the GLA needs a strong left voice, which could be achieved if Galloway was elected to it.

Despite the original success of Respect in 2004 and 2005, it has grown less well than it should have done. Partly this was attributable not only to the organisational stranglehold of the SWP, but also due to the distrust that the SWP are held by many activists within the broader labour movement.

But also George Galloway had in the past limited appeal to trade unionists, and the Big Brother episode did make many doubt his commitment to serious politics. Paradoxically, though it seemed like a howler to many of us at the time, Celebrity Big Brother did lead to George’s opportunity to take on the Talk Sport radio show that has been a phenomenal success. Time and time again now, when I am talking to trade union or labour movement activists,  they tell me that they listen to Galloway’s show and are deeply impressed by it. Galloway has achieved a big personal audience among the working class, and many are broadly sympathetic to his politics. So paradoxically, over the long term, the Celebrity Big Brother decision has probably had more positive than negative consequences.

For the general public, George Galloway’s elicits both strong positive and negative responses, but broadly his personal and political reputation is higher now than it was in 2005: whether that transfers into votes, we don’t yet know.

The rally has been called by the Londoners for Peace.

Speaking on BBC Radio 4's The World at One this afternoon, Livingstone said he did not trust the way YouGov collected their data.

"I have great doubts about opinion polls based on people you can reach over the internet as one third of Londoners are not on the internet," he said.

The mayor's campaign announced this morning that it was launching an official complaint against YouGov's polls on the London election, saying that their methodology was "fundamentally flawed".

A spokeswoman for the Labour candidate said in a statement: "YouGov's polls are misleading the public and we have therefore decided to make a formal complaint."

She said that the market research company was weighting responses from certain age groups in London and did not take into account the "much larger" ethnic-minority population in the capital.

"These and other mistakes mean that they consistently overestimate support for the Conservatives in London compared to established polling techniques," she said.

The mayor's office made a similar challenge to a YouGov poll last week, which put him 10 points behind Johnson. Livingstone complained that the results were "implausible" as the polls had assumed that the proportion of black and Asian voters in London was the same as for the UK as a whole.

The Guardian's last ICM poll on the London mayoral race, published on April 2, had Johnson on 51% to Livingstone's 49%, once second preferences had been allocated under the capital's alternative-vote system.

It could not be further from the truth to say that there are no serious differences between the contenders in the London mayoral election (The Weary and warier, March 18; Ken and Boris play Big Brother, March 19).

The choice between Boris Johnson's nightmare vision and our policies could not be clearer. Boris Johnson opposed the minimum wage, and supported George Bush in opposing the Kyoto treaty. He would scrap the affordable housing requirement and the £25 CO2 charge on gas guzzlers, and has called the low emission zone to cut air pollution "the most punitive, draconian fining regime in the whole of Europe". He backs nuclear power and nuclear weapons.

Because Boris Johnson's anti-green and anti-social agenda is a throwback that means he cannot be trusted with London's future, we have come together to call on our supporters to use their second-preference votes for each other. The choice is very clear - go backwards with Boris Johnson, or make sure London continues to have a green mayor by voting for for our candidacies.
Siân Berry, Green party candidate
Ken Livingstone, Labour party candidate

Simon Hoggart may not be able to slot a bus ticket between Ken Livingstone's and Boris Johnson's policies, but I could drive a fleet of bendy buses through the gap - sideways.

On housing, Ken is for 50% of new homes to be affordable. That doesn't go far enough, but my constituents in overcrowded Tower Hamlets know that scrapping that target, Johnson's policy, will make it less likely that their children will ever get a home in the capital.

Whatever differences you have with Ken - and I have many - it is incredible to say he's of a piece with Johnson, especially this week, the fifth anniversary of the disastrous invasion of Iraq. Ken opposed that war; Johnson supported it and adheres to the neoconservative lunacy that underpins it.

Over the past eight years the anti-war and anti-racist movements have had a friend in City Hall. I want a mayor who welcomes Muslim leaders who are arguing for engagement in the political process, rather than one who bans them from entering the country, as Johnson and David Cameron demanded and Gordon Brown went along with recently.

Ken's under attack not for the things he's done wrong, but for the policies that have angered the Tory right. That's why every progressive Londoner should support him against Johnson.

It's said that Ken doesn't take notice of the London assembly. That's because most of those on it are eminently unnoteworthy. Most people in London can't name a single assembly member.

I'm standing for the assembly for Respect to change that. If I and my colleagues are on the assembly, Ken won't be able to ignore us. We'll support him when he's in the right, and hold him to account when he's not.
George Galloway MP, Respect, Bethnal Green & Bow

Now Banksy, the secretive street artist, has turned his attention to domestic issues, agreeing to support London mayor Ken Livingstone's bid for re-election.

The artist, whose works have fetched more than £300,000 at auction, is one of more than 20 leading figures from the art world who are donating work to the Bid for Ken auction. Yesterday Livingstone, who is standing for re-election in May, said: "London is a city where the arts flourish. Artists in all fields make a central contribution to how we see our city and our society as a whole."