By Peter Griffiths
LONDON (Reuters) - A rich British businessman said on Monday he would "do whatever it takes" to help the UK Independence Party fight next year's European Union polls, where gains for the anti-EU group could hurt Prime Minister David Cameron's chances of winning a second term.
UKIP, a right-wing group that wants to leave the EU and impose tighter immigration controls, is leaching support from Cameron's Conservatives and poses one of the biggest obstacles to his re-election at a national poll in May 2015.
A strong UKIP performance in the European parliament elections in May could widen historic Conservative divisions over Europe that Cameron had hoped to heal in January with a promise of a referendum on membership of the 28-nation bloc.
Polls suggest Britain would vote to leave the EU if a referendum were held today. However, if Cameron succeeds in his goal of reforming London's ties with the EU, they would opt to stay in the bloc, one poll showed last week.
Paul Sykes, a Eurosceptic former Conservative supporter, said he wanted to force the main parties to "abandon their slavish support for the EU" and bring forward the referendum, which Cameron says will take place by the end of 2017.
"We have one last chance to stop the gradual erosion of our national independence. And that chance comes with the European elections," Sykes said in a statement. "UKIP are the last best hope for Britain. I'm prepared to do whatever it takes to propel them to victory next year."
Sykes, a property and internet entrepreneur whose fortune was once estimated at 650 million pounds ($1.05 billion), did not say how much he would donate to UKIP.
Although UKIP has no seats in the British parliament, it has 13 in the European parliament and took a quarter of the votes cast in local elections in May.
UKIP won 16.6 percent of the vote at the last European polls in 2009, behind the Conservatives on 27.9 percent and ahead of Labour on 15.8 percent.
Its leader Nigel Farage told Reuters in July his party could win the European elections, after years on the fringes of British politics.
A former supporter of Conservative Prime Minister Margaret Thatcher, whose downfall was in part due to party bickering over Europe, Sykes said he was campaigning against a loss of sovereignty to Brussels and a rise in immigration.
($1 = 0.6215 British pounds)
(Editing by Alistair Lyon)