LONDON: Prime Minister Gordon Brown was fighting for his political life on Thursday as the public voted in European and local elections that could push him closer to the brink.

An email letter was being circulated around his Labour Party's lawmakers calling for him to quit, while a looming cabinet reshuffle could reportedly see senior ministers revolt if he demotes them.

Speculation that Brown was preparing to step down sent the British pound crashing against the euro and dollar. Brown's spokesman described the rumour as "complete nonsense".

Addressed to the prime minister, the email highlights Brown's "enormous contribution to this country and to the Labour Party, and this is very widely acknowledged".

"However," it added, "in the current political situation, you can best serve the Labour Party and the country by stepping down as party leader and prime minister, and so allowing the party to choose a new leader to take us into the next general election."

Brown is struggling to assert his authority after four government ministers quit in two days, two of them cabinet members badly damaged by an expenses scandal that has rocked the British parliament.

Business Secretary Peter Mandelson urged colleagues not to sign the letter against Brown.

"British politics is in a bad old state, nobody is happy and it's affecting all the parties," he told the BBC, admitting that lawmakers were in a "grumbly mood".

"Don't please, through your actions, make it any worse for the Labour Party than for the other parties who have all got to come to grips with this crisis affecting British politics."

In power since 1997, the Labour party has borne the brunt of public outrage at revelations of dodgy expenses claims made by lawmakers, a row made worse by the fact Britain is struggling to climb out of its worst recession in decades.

Britain's 72 seats in the European parliament were up for grabs in Thursday's elections, while voters in various parts of England were also choosing 2,318 local councillors and three mayors.

Opinion polls suggest Labour could finish behind the main opposition Conservatives -- tipped to win the next general election, due by mid-2010 -- the Liberal Democrats, and even fringe eurosceptics the United Kingdom Independence Party (UKIP).

Such a poor showing for Labour would pile further pressure on Brown, who has been repeatedly challenged by opposition parties to call an election now.

A spokesman for Brown's Downing Street office said the prime minister was spending the day there working.

He "is focused on getting the job done on renewing trust in our political system and our democratic processes and taking the kind of decisions that will help the British people get through difficult economic circumstances," he said.

Communities Secretary Hazel Blears, who faced criticism over her expenses, resigned on Wednesday, and Home Secretary Jacqui Smith said she would step down at the next cabinet reshuffle, which could come as soon as Friday.

There is speculation that the prime minister -- who took over from Tony Blair in June 2007 -- wants to replace Finance minister Alistair Darling and possibly Foreign Secretary David Miliband.

However, they are reportedly resisting attempts to move them.

The polls close at 10:00 pm (2100 GMT). The local election results are expected Friday, but the results of the European elections are not due to be published until Sunday, in line with other EU member states.

A YouGov poll for The Daily Telegraph newspaper published Thursday suggested that among people certain to vote, 26 percent would back the Conservatives, 18 percent UKIP, 16 percent Labour and 15 percent the Liberal Democrats.

The survey of 4,014 people conducted June 2-3 put the Green Party on 10 percent and the far-right British National Party on five percent, which could be enough to hand them their first European Parliament lawmaker.