NICK Clegg and Danny ­Alexander have stepped up their campaign against Conservative eurosceptics, denouncing them as "unpatriotic".

Mr Alexander, the Liberal Democrat Chief Secretary to the Treasury, warned that those who wanted to leave the European Union were opposed to economic growth and acting against the best interests of the country.

His party leader went even further accusing "large parts" of the Tory Party of being "unpatriotic" for advocating British withdrawal.

The comments led to accusations from Nigel Farage, leader of Ukip, that the LibDems were "rattled" by the news that the eurosceptics have secured the financial backing of multi-millionaire Paul Sykes.

Mr Sykes, a former Conservative Party donor who has previously been estimated to be worth £650 million, has pledged to pay for Ukip's campaign during next year's European elections.

Speaking to journalists, Deputy Prime Minister Mr Clegg said that seeking EU exit was "a betrayal of the national interest."

He said that withdrawal would cost jobs and economic prosperity and leave Britain weaker as a country.

In a speech Mr Alexander said: "If you are anti-Europe, you are anti-business, anti-growth, acting against the best interests of your country."

He also issued a rallying call to businesses to make their voices heard on the issue.

Mr Farage responded: "These ridiculous comments from Mr Clegg demonstrate just how worried the pro-EU establishment are becoming.

"The news Paul Sykes will be supporting the Ukip European election campaign clearly has them worried and already we're seeing pathetic attacks of this nature."