The "cash for honours" inquiry was launched last year amid claims that political parties had illegally offered seats in the unelected upper House of Lords to financial supporters.

Blair left office on Wednesday and was replaced by former finance minister Gordon Brown, who was unveiling his ministerial team as the information about Blair emerged.

He had previously been interviewed twice as a witness and members of his cabinet have also been quizzed. Blair was the first sitting prime minister to be questioned as part of a criminal inquiry.

A spokeswoman for London's Metropolitan Police, which is leading the investigation, told AFP that they were "not prepared to discuss" the report. Blair's representatives were not immediately contactable.

Four people have been arrested during the probe, including two of Blair's closest aides, Lord Michael Levy, who was Labour's chief fundraiser and Middle East envoy, and Ruth Turner, a senior Downing Street official under Blair.

Levy and Turner, plus businessman and Labour Party backer Sir Christopher Evans, remain on bail. They deny any wrong-doing and no-one has been charged in the case.