LONDON (Reuters) - British Prime Minister Gordon Brown will face growing pressure to quit if European and local elections on Thursday go as badly as feared.

Britain's Prime Minister Gordon Brown leaves Downing Street on his way to Prime Minister's Questions at the Houses of Parliament in London June 3, 2009. Brown will face growing pressure to quit if European and local elections on Thursday go as badly as feared. REUTERS/Stefan Wermuth

Brown’s reputation, already battered by a deep recession, has been knocked further by a parliamentary expenses scandal and the resignation of two cabinet ministers this week.

His ruling Labour party lagged by as much as 20 points in opinion polls behind the opposition Conservatives led by David Cameron before the elections, the last major popular test before a parliamentary election due by this time next year.

Media reports said up to 75 Labour members of parliament (MPs) -- around a fifth of the total -- were ready to sign a letter calling for his resignation.

Business Secretary Peter Mandelson called for calm, saying a plot would only “make things worse for the Labour Party”.

“British politics is in a bad old state, nobody is happy and it is affecting all the parties,” he told BBC television.

The impression that Brown is struggling to keep control of his party increased on Wednesday when a second cabinet minister said she was stepping down, pre-empting an expected cabinet reshuffle Brown had hoped would revive his flagging fortunes.

Communities Secretary Hazel Blears joined Home Secretary (interior minister) Jacqui Smith in announcing her resignation.

Both had been tipped for the axe in any reshuffle, but it sparked talk of a revolt against Brown.

“DEAR GORDON”

A Labour politician told Reuters he believed a letter calling on Brown to step down was in the works.

The Sun newspaper, Britain’s biggest selling tabloid, printed what it said was the wording of the letter:

“We are writing now because we believe that in the current political situation you can best serve the Labour Party and the country by stepping down,” it said in a letter addressed to: “Dear Gordon”.

With Labour’s popularity at such a low ebb, Brown’s job would be a poisoned chalice. Health Secretary Alan Johnson, tipped as the favourite to succeed him, gave the prime minister his support on Wednesday.

Opinion polls indicate Labour could be pushed into fourth place in the European Parliament election as voters express their fury over lavish expenses claims.

All parties have been hit by the scandal, in which members of parliament have claimed taxpayers money to pay for everything from floating duck houses, to horse manure, to cleaning a moat.

Voter disillusionment is expected to boost support for far-right parties such as the British National Party (BNP).

Any change of prime minister would add to the clamour for an early election to replace a discredited lower house of parliament. More than a dozen MPs have said they will not stand for re-election after details of their expenses were revealed.

Brown had been expected to wait until May 2010 to call an election, hoping the economy will start to recover by then.

A YouGov poll for the Daily Telegraph said among people certain to vote in the European polls, Labour would get just 16 percent support, ahead of the Liberal Democrats on 15 percent and behind the United Kingdom Independence Party (UKIP) on 18 percent. It put Conservative support at 26 percent of the vote.

Labour also faces a rout at local level, where 18 million eligible voters will decide on the composition of 34 local authorities. The party could lose control of four councils in its traditional heartlands in the northwest and Midlands.

Results of the local elections will be announced from the early hours of Friday, while the European results will not be released until Sunday night.