But the party's new leader accused his predecessor of being motivated by bitterness.

UKIP founder Dr Alan Sked, a professor of international history of the London School of Economics, said Mr Hague "deserved to be rewarded" for making the Tories more Eurosceptic.

William Hague "deserves to be rewarded", the UKIP's founder says

He described his former colleagues as having "no coherent sense of principles".

But UKIP leader Michael Holmes said Dr Sked's support for the Conservatives followed a failed attempt to set up another fringe party.

This came after an acrimonious split involving accusations of right-wing extremism and libel threats between Dr Sked and other UKIP members.

Mr Holmes told BBC News Online: "He left the party in a high fit of pique because people wouldn't support him.

"He was going to stand against us but couldn't find any money or backers to support him."

In contrast, the UKIP, which has about 8,000 members, has raised £500,000 to fight its European election campaign, Mr Holmes said.

Dr Sked left the UKIP after the 1997 general election contest in which its core demand that Britain leave the European Union and its campaign were largely overshadowed by Sir James Goldsmith's Referendum Party.

Michael Holmes: Comments motivated by "bitterness"

He has since criticised the party for its decision to take up any seats it wins in the European Parliament election.

"Alan Sked I'm afraid is bitter," Mr Holmes said. "His main thrust is that we're being unprincipled in taking the seats, but all this bitterness is behind it."

But Dr Sked told The Daily Telegraph his change in position stemmed from the Conservatives increasingly anti-European line.

"If you feel the Tories have moved in the right direction since the last election, which I feel they have, then William Hague deserves to be rewarded on that," he said.

Mr Holmes pointed out that the Conservatives had only promised not to join the European single currency within the next eight years and wanted to remain in the European Union.