Ray Ruddick and Janet Kidd are listed by the Electoral Commission as having given large sums to the party over the past five years, culminating in a gift of £80,000 from each of them on July 10 this year.

Yet reports say that when approached Mr Ruddick initially denied having given the party money and said neither he nor Mrs Kidd were aware of the donations.

In a later statement, a paper says he confirmed the £80,000 donations, but said they were the first that he and Mrs Kidd had given.

Reports claim Mr Ruddick, a builder, drives an old Transit van and lives in a former council house in Newcastle, said: "I can't stand Labour. I can't stand any politicians."

According to the Electoral Commission, Mr Ruddick has donated £196,850 to Labour and Mrs Kidd £185,000 since 2003.

Between them, they are listed as having given the party £222,000 since Gordon Brown became leader, making them his third biggest donors after Lord Sainsbury and businessman Mahmoud Khayami.

Both are thought to be linked with David Abrahams, a wealthy property developer and prominent Labour figure in the North-East.

Mr Abrahams reportedly declined to comment on whether he had funded the donations.

A Labour spokesman has confirmed that the party's General Secretary Peter Watt had been asked to look into the gifts.