CARDIFF/LONDON (Reuters) - New polls on Monday showed the Liberal Democrats surging in popularity ahead of a May 6 election as the two larger parties tried to fend off the unexpected challenge.
The election has been thrown wide open since a strong performance by Liberal Democrat leader Nick Clegg last Thursday in a live TV debate with Prime Minister Gordon Brown and frontrunner David Cameron of the Conservatives.
In the latest of a series of shock poll results, a YouGov survey published in the Sun newspaper found the Liberal Democrats, or LibDems, in first place.
An ICM poll for the Guardian put them second, ahead of Labour, which has been in power for 13 years.
Cameron, 43, has long been the favourite to be the new prime minister, but he needs his party to win an overall majority in parliament and the LibDems could deprive him of that if they are able to sustain the momentum until May 6.
"I want to be the next prime minister," Clegg, 43, told a news conference in the Welsh capital Cardiff.
That remains a very far-fetched scenario.
What matters most in British elections is not the share of the national vote won by the parties but the number of seats they win in parliament. The LibDems are unlikely to win as many seats as Labour or the Conservatives despite their poll surge.
"VOTE CLEGG, GET BROWN"
But a strong LibDem performance could mean that instead of a clear Conservative win allowing them to govern solo, the election could produce a "hung parliament" in which no party has an overall majority of seats and can rule alone.
Such a result, known as a "hung parliament" and not seen in Britain since 1974, could give the unpopular Brown, 59, a chance of staying in power if he could tempt the Lib Dems into an alliance. Failing that, a Conservative-Lib Dem pact is possible.
In a sign that the Lib Dem bounce may have alarmed the Conservatives, they scrapped a planned campaign broadcast attacking Labour in favour of a more personal clip in which Cameron sought to reclaim the message of change from Clegg.
"The only way we're going to get that change is through a clear, decisive result in this election ... We need a new Conservative government to come in with a strong mandate," Cameron says in the new version, which was posted on YouTube.
The LibDems would appear to be more natural bedfellows with Labour, but such an alliance would be hard for the LibDems to justify if the Conservatives won more votes than Labour, given long-standing LibDem demands for proportional representation.
Cameron's message to voters on Monday could be summarised as "Vote Clegg, get Brown."
"You could easily wake up on May 7 and find literally you are stuck with what you've got, stuck with Gordon Brown, stuck with the deficit, stuck with an economy that isn't moving and nothing has changed," he said at campaign event in London.
Sterling fell sharply on Monday on fears that a hung parliament could lead to haggling between the parties and delays in tackling the deficit, which is running at 11 percent of GDP.
"What the markets want, what the people of this country want is, they want competence, they want certainty, they want a government that knows what it's doing," said Chancellor Alistair Darling, playing the experience card for Labour.
(Writing by Estelle Shirbon; editing by Andrew Roche)