Chancellor Gordon Brown has launched an inquiry into the leaking of a letter suggesting he was opposed to key parts of the Turner report on pensions.
Mr Brown: Opposes pensions earnings link
The leak sparked a huge political row, with the Conservatives accusing Mr Brown of trying to "sabotage" reforms.
Mr Brown insisted he was not anti-reform but could not back unaffordable proposals.
Lord Turner is expected to say people should work to the age of 67 to pay for a rise in the basic state pension.
Mr Brown has always fiercely resisted such calls, which would involve scrapping means-tested pensions credit and restoring the link with earnings.
In his letter, details of which appeared in Thursday's Financial Times, he effectively warned Lord Turner he had got his sums wrong.
It is understood to have angered Lord Turner, who has spent three years on the government-commissioned report, which is due to be published on Wednesday.
A Treasury spokesman said the letter had been circulated to a very small number of people in the Treasury, Downing Street and the Department of Work and Pensions - probably no more than half a dozen in each department.
Mr Brown has asked Treasury permanent secretary Nicholas Macpherson to conduct the inquiry into how it was leaked to the press.
The Cabinet Office is not conducting the inquiry although a spokesman said it had no objection to it.
Whitehall leak inquiries rarely succeed but the Treasury believes the small circulation of the letter could help pin down the culprit.
Earlier, Downing Street attempted to distance itself from suggestions the leak had originated in its offices.
The prime minister's official spokesman, attending the Commonwealth Heads of Government Conference in Malta with Mr Blair, said: "I can categorically deny, as far as my knowledge goes and those I have spoken to in Number 10, that we were responsible for the leak."
He said Number 10 wanted to see Lord Turner's report - which is due to be published on Wednesday - considered in its entirety.
"We believe that it is a serious analysis that deserves serious treatment, not one-sided leaking," he said.