The forthcoming autobiography by the former paymaster general may reveal that he made a large contribution to a blind trust that helped fund Mr Blair's office before the election.
The identities of contributors to the trust are known only by the trustees and have never been disclosed.
But it is widely known that Mr Robinson was a key financial backer of the Labour Party after Mr Blair became leader. He also made big donations to Gordon Brown's office before Labour was elected.
Reports that the donation to Mr Blair's office was part of a "war fund" to fight a possible leadership challenge by Mr Brown were swiftly dismissed last night as "completely untrue".
"It is well known that Tony Blair's office was partly funded by a blind trust," said a Downing Street spokesman. "The very nature of a blind trust means that the donations made in it were not and are not known."
There is intense speculation at Westminster about the contents of the former minister's autobiography.
There have already been reports that Peter Mandelson asked Mr Robinson for the pounds 373,000 loan to buy his London home, rather than the accepted version - that the money was offered.
Downing Street has been trying to head off damage from the forthcoming book in recent weeks. Mr Blair has reportedly asked Anji Hunter, his personal assistant, to help persuade Mr Robinson to "pull his punches".
MPs fear that Mr Robinson, widely regarded as an ally of Mr Brown, the Chancellor, may lift the lid on the Labour Party's finances before the last election.
Mr Robinson, who was made a minister after Labour took office, resigned amid controversy over the loan to Mr Mandelson. His ministerial career was dogged by criticism of the offshore trusts he held.Reuse content