Tycoon Paul Sykes backs UKIP European election campaign
One of the UK's wealthiest men has pledged "whatever it takes" to ensure the UK Independence Party triumphs in the 2014 European Parliament elections.
Eurosceptic Paul Sykes said UKIP was the "last best hope for Britain" and he would help fund its election campaign.
Mr Sykes, who has formerly backed the Conservatives, made donations to UKIP between 2001 and 2004. His latest funds will pay for UKIP's advertising.
UKIP leader Nigel Farage said Mr Sykes' backing was a "significant boost".
But Deputy Prime Minister Nick Clegg accused the party of being "unpatriotic", arguing that leaving the EU would damage the UK's prosperity and undermine its position in the world.
Mr Sykes, who is estimated to have a fortune of around £650m, has given no indication of how much he is prepared to donate on this occasion, but said he believed the European elections were "the one last chance to stop the gradual erosion of our national independence".
"If, as I hope and believe, UKIP score a stunning national victory, then the leaders of the other main parties will have no choice but to abandon their slavish support for the EU," he said in a statement.
"Nigel Farage and UKIP are the last best hope for Britain. I am prepared to do whatever it takes to propel them to victory next year."
He told BBC Radio 4's Today programme the "awareness" campaign would "engage the British public in a subject that is very important to them".
He said he hoped success for UKIP at next year's election would lead to an early referendum on the UK's membership of the EU rather than "hanging about to 2017".
"I think it's time to step up and bring the referendum forward to 2015," he said.
Conservatives say a vote for UKIP in the 2015 general election would make a referendum less likely as it would increase the chances of Labour - who oppose a public vote on the issue - forming the next UK government.
Mr Sykes said he was not concerned about "party politics" - telling the BBC's Daily Politics he was not a member of any party and did not vote - but he acknowledged that a strong showing by UKIP next year was likely to "bring the referendum forward".
"I have decided there is only one game in town and that is UKIP, who has declared quite clearly that if we vote for them in the next European elections, we would stand a good chance of negotiating ourselves out of the EU."
He suggested Mr Cameron's ambition to renegotiate the UK's membership prior to a 2017 referendum would not lead anywhere because other EU leaders knew that he wanted to stay in the EU regardless of the outcome.
"I have listened to the Conservative Party for 25 years and I was a member for 27 years," he added.
"I listened to them on the euro and if we had not stepped in - me and Jimmy Goldsmith - you would be sitting here with euros in your pockets."
Mr Farage said Mr Sykes had a "long record of defending British democracy" and his donation would help his party cause an "intended earthquake" in British politics.
UKIP has reached unprecedented heights in the opinion polls under Mr Farage, coming second in the European elections in 2009 and winning hundreds of seats in May's local elections.
The party won 13 seats in the European Parliament after winning around 16.5% of the vote in 2009, pushing Labour into third place.
But, at the 2010 general election, support dwindled to 3.1% and UKIP did not win a Westminster seat.
Mr Sykes was previously a strong supporter and backer of the Conservatives under Margaret Thatcher in the 1980s but broke with the party in 1991 over John Major's stance on the Maastricht Treaty.
In the 1997 general election, he selectively funded individual Eurosceptic candidates.
In 2000 he briefly returned to the Tory fold under William Hague, only to be expelled the following year over his hardline views on Europe.
Mr Sykes is reported to have given millions of pounds to various Eurosceptic causes over the years.
He declined to say, on Daily Politics, whether he would help fund the UKIP general election campaign, saying: "I have only got one target and that is to win the European elections."
At his monthly press conference, Nick Clegg said UKIP's stance on the EU did not "represent the national interest".
He said: "The Conservative Party seems to be flirting with exiting altogether and Labour seems to have lost its convictions."
Mr Clegg said that, as Liberal Democrat leader, he would "relish" the debate with UKIP ahead of the European elections. He accused his rival party of taking an "unpatriotic approach", saying: "In a footloose global world we are stronger together than we are apart."