Downing Street has denied that information about the cash-for-honours affair was leaked by its staff.
The BBC can now say the e-mail that triggered the investigation into an alleged Downing Street cover-up was sent by Number 10 aide Ruth Turner.
An injunction on Friday prevented the BBC from reporting an e-mail between two members of the PM's inner circle.
It was sent to Tony Blair's chief of staff, Jonathan Powell, and concerned Labour's chief fundraiser Lord Levy.
The prime minister's official spokesman told reporters that suggestions of a No 10 leak were "just plain wrong".
The BBC is still barred from revealing the contents of the e-mail.
The police have been investigating allegations that honours were given in exchange for loans. Four people have been arrested. All deny wrongdoing.
The injunction preventing the BBC from broadcasting a story about this e-mail - granted on Friday night - was amended on Monday afternoon.
The spokesman said on Monday that his assertion was not based on his "personal hunch" but "because there are inaccuracies in the reports which means it couldn't have come from No 10".
He refused to say what those inaccuracies were.
The police said its investigation was on-going and that the Crown Prosecution Service would not reveal "any of its deliberations on this case".
"When the CPS has made its decisions, they will be announced publicly," the police said in a statement.
