One of the Conservatives' biggest financial backers is "working from within" the party to try to shift it in a more eurosceptic direction, UK Independence Party leader Lord Pearson of Rannoch claims.
Lord Pearson said that Henry Angest was one of a group of Tories who were "very disappointed" that leader David Cameron has not offered a referendum on quitting the European Union.
The Observer revealed that companies linked to the Swiss-born banker have lent or donated almost £7 million to the Conservatives over the past decade.
Lord Pearson confirmed that Mr Angest had also given money to his eurosceptic think-tank Global Britain, which monitors BBC broadcasts for bias over Europe.
The Ukip leader told BBC1's Andrew Marr Show: "He is a eurosceptic, there's no doubt about it. He has funded in the past my Global Britain think-tank.
"Henry is someone who would like the Conservative Party to be more eurosceptic. He is someone who is - and I think there are many of my friends who are - working from within the Conservative Party to achieve that.
"All of them and most of the Conservative grassroots - and us - are very disappointed that David Cameron didn't deliver the referendum on our membership of the European Union that he promised."
The private bank Arbuthnot Latham, in which Mr Angest holds a majority stake, lent the Tories £5 million last year, boosting their election war chest. And Mr Angest has donated £1.2 million since 2001 through a party called Flowidea and lent a further £500,000 - since repaid - through Wyler Investments.
A Conservative source said that Mr Angest held no official position within the party.