* Britain holds local elections on Thursday
* Ruling Conservatives expected to lose hundreds of seats
* Anti-EU party could win dozens of seats
* Parties test political climate before 2015 national vote
Britain's ruling Conservatives derided the rival UK Independence Party as a "collection of clowns" on Sunday as they tried to stop supporters switching to the surging anti-European Union movement in local elections this week.
Thursday's vote in England and Wales offers parties a chance to test the political climate before a national election in 2015 at a time when Conservative strategists fear UKIP will split the centre-right vote.
Ken Clarke, a prominent Conservative and government minister, said he agreed with Cameron's assertion that UKIP had "fruitcakes and closet racists" in its ranks and that it tried to exploit voters' fears.
"These are very difficult times. The political class is regarded as having got us into a mess and the last government left chaos behind them," he told Sky News. "It's very tempting to vote for a collection of clowns."
Battling to kick-start a tepid economy and to cut a big budget deficit, Cameron is banking on a rebound before 2015. But with no strong recovery in sight he faces losing hundreds of the more than 2,000 council seats his party is contesting.
A bad result in the vote - held largely in rural English counties and in one Welsh area - could prompt some Conservative MPs to question Cameron's leadership, though he has ridden out such dissent before.
Campaigning on a promise to take Britain out of the EU and to end "open-door" immigration, UKIP has seen its poll rating oscillate between 11 and 17 percent, overtaking Cameron's junior Liberal Democrat coalition partner at times.
"The trouble with UKIP really is it's just a protest party," said Clarke. "It's against the political parties ... it's against foreigners ... but it doesn't have any very positive policies. They don't know what they're for."
As its popularity has grown so too has public scrutiny.
It was forced to suspend one of its more than 1,700 candidates over his support for a group that has organised protests against Muslim immigrants. Another candidate resigned over his past membership of a far-right group and a third was suspended over an anti-Semitic online row.
UKIP has said it is the victim of a "reprehensible" smear-campaign by the Conservatives, who it says are running scared.
"They must be utterly terrified that their shallow approach to government is being seen through by the public," said Nigel Farage, the party's leader.
Leaked emails published by The Observer newspaper on Sunday suggested UKIP was worried it had few credible policies beyond its opposition to the EU and immigration, saying its members were struggling to coalesce around other ideas. The party said the emails were evidence of a lively internal debate.
Analysts say UKIP's popularity has already prompted the government to harden its stance on Europe and immigration.
"Long-term national interest must be our guide, not short-term politics," he wrote in the Independent on Sunday.