City boss Michael Davis’s cash gift gave the party a major boost as the campaign entered its final days.

Labour MP Karl Turner said: “Once again David Cameron has questions to answer about the favours granted to his fatcat donors.

“The Tory Party is bankrolled by big money in the City, and the PM always seems to look after his own.”

The donation on April 27 has been revealed in figures released by the Electoral Commission.

On June 12 it was announced Davis, 57, was one of four Tory donors being knighted in the Queen’s birthday honours.

His donations to the party now total nearly £1.5million. He declined to comment but there is no suggestion he has done anything wrong.”