* Local elections being held in England and Wales
* Single national parliamentary seat also up for grabs
* Ruling conservatives forecast to lose hundreds of seats
* Anti-EU party predicted to do well, as is Labour
Britain's ruling Conservatives are set to lose hundreds of seats in local polls on Thursday that will go some way to measuring the threat the surging anti-European Union UK Independence Party (UKIP) poses to their hopes of re-election in 2015.
Even in towns like Ashford in southeast England, which has returned a Conservative MP to the national parliament at every election since 1945, surveys suggest UKIP could win up to one fifth of the votes.
History shows Britons often use mid-term council elections to punish their favoured party for perceived failings by temporarily forsaking it only to return when it really counts.
But polling data shows UKIP, which wants to radically tighten immigration rules into Britain, is luring Prime Minister David Cameron's traditional supporters away.
That trend risks splitting the centre-right vote in 2015, making Cameron's task of beating the main opposition Labour party even harder.
The Conservatives, the senior partner in a two-party national coalition, trail Labour by up to 10 percentage points in opinion polls, but they are banking on an economic rebound by 2015 to lift Britain from its torpor.
If a national election were held today, Labour would win.
"I've been a Conservative all my life but I'm going to vote for UKIP," said Bill Newton, 76, a retired businessman, out shopping in Ashford's futuristic tented mall. "I want the Conservatives to get the message that they need to change."
More than 2,000 council seats in largely English rural counties and in one Welsh area are up for grabs on Thursday. One national parliamentary seat is also being contested in northern England where UKIP hopes to come second to Labour.
Heavy Conservative losses could renew pressure on Cameron's leadership ahead of a national election in 2015, and the vote is being seen as one of the last chances to test the political climate before that ballot.
UKIP WANTS END TO "OPEN DOOR" IMMIGRATION
Campaigning on a promise to take Britain out of the EU and to end "open-door" immigration, UKIP's policies appeal to many traditional Conservatives who feel Cameron has taken their own party in too liberal a direction.
But though UKIP has surged in the polls, it has no MPs in the national parliament and Thursday's election will indicate if its swelling poll support translates into votes. Full results of the council ballots will not be known until Friday.
"One local poll put our support at 60 percent," Norman Taylor, the UKIP candidate for Ashford Central, told Reuters in an interview. "I don't believe we'll get that, but we should get around 20 percent. From now on we're going to be a dominant force in politics."
The main reason for UKIP's growing popularity is its immigration policy, he said.
"Say NO to mass immigration," proclaim colourful leaflets being handed out to voters on the streets of Ashford.
Taylor, 74, said Ashford and its periphery, which has a population of about 80,000 and is close to the tunnel that links Britain to France, had been "particularly hard hit" by immigration.
An area the former government designated a growth zone, he said it had seen an influx of British migrant workers moving from London for lower housing costs coupled with the arrival of foreign immigrants, particularly from Eastern Europe.
"Everything here is crumbling in every way," he said. "Public services can't cope. They let everyone in and only then did they start to think about the infrastructure."
Taylor said his views and those of his party were not racist but reflected the concerns of many local blue collar workers.
"I've got nothing against them (immigrants). The only problem is we can't handle the numbers."
The background of some of the party's candidates has stirred controversy, however. Several have been suspended after it emerged they had once belonged to far-right groups and a photograph of one candidate making what looks like a Nazi salute has been plastered on newspaper front pages.
Nigel Farage, the party's leader, has said UKIP was unable to vet all of its some 1,700 candidates properly, saying a few undesirables had got through.
On Ashford's main shopping street there are mixed feelings about UKIP, especially from the town's large Nepali diaspora.
A British army battalion of Gurkha soldiers is based nearby and many ex-soldiers have settled in Ashford.
One retired Gurkha who declined to be named said he felt uneasy. "I'm not convinced by UKIP," he said, saying he feared its policies could stoke hostility towards his own community.