* Scandal erodes support for main parties
* Speaker of House of Commons to deliver statement
* Business Secretary says "dangerous time for politics"
By Keith Weir
LONDON, May 18 An expenses scandal is eroding support for Britain's three main political parties, a poll showed on Monday, and has brought calls for parliament's most senior figure to step down.
The top-selling Sun tabloid said a general election due by the middle of next year should be held immediately after days of disclosures about lawmakers' questionable and sometimes lavish expenses brought British politics into disrepute.
"Voters have had enough of this Government, enough of greedy MPs, enough of a Commons Speaker who has turned the Mother of Parliaments into the mother of all shyster politicians," it said in an editorial headlined "Give Britain an election ... now".
Prime Minister Gordon Brown is certain to resist calls for an election, with his ruling centre-left Labour Party trailing the opposition Conservatives in polls and the economy in its worst recession since World War Two.
The Conservatives had a 16 percent lead over Labour in an opinion poll published in the Daily Telegraph on Monday. The Conservatives were on 39 percent, Labour 23 percent, the Liberal Democrats 19 percent and other parties also 19 percent.
The support for parties beyond the main three had jumped nine points from the previous month, adding to speculation that fringe groups like the Greens, the anti-European Union UK Independence Party and far-right British National Party (BNP) will show big gains in European and local elections on June 4.
Britain's financial markets have yet to show any response to the scandal. European and local government elections rarely cause market ripples regardless of results. However, a poor showing for Labour would reopen speculation about whether Brown should lead the party into a general election next year.
Investors are worried about Britain's ballooning debt but, given opinion polls, will not be surprised if Labour loses next year's election.
SPEAKER FACES CRITICS
An opposition Conservative politician has prepared a motion of no confidence in Michael Martin, the Speaker of the House of Commons (lower house), over his handling of the crisis. If ousted, Martin would be the first Speaker to be sacked since 1695. The position of a Speaker or presiding officer in British politics dates back to the 13th century.
As well as keeping order in the lower house of parliament and calling MPs to speak, the Speaker, who wears a black silk robe over his suit, is the house's highest authority who must have support across the political spectrum.
Martin, a veteran member of the ruling Labour party, has been criticised for opposing transparency on lawmakers' expenses and failure to overhaul a flawed system. He is due to make a statement to the house on Monday at around 1430 GMT in which he is likely to set out his plans for reform.
The Daily Telegraph has got hold of a disc containing details of expense claims and has been publishing damaging reports of claims for moat cleaning, an adult film and dog food, as well as for mortgages that have been paid off.
The image of all parties has suffered, but Labour has been worst hit because it has been in power for the last 12 years and was already on the ropes over the economic crisis.
Labour has suspended two MPs and one of its junior ministers has stepped down pending an investigation into his finances.
Business Secretary Peter Mandelson said in a speech on Monday that the combination of financial and political crisis made it "a dangerous time for politics".
"I know that people are really angry and appalled by the sort of disclosures that are being made ... and it's totally fair that people are angry about it," Mandelson told Sky News.