There was increasing speculation among MPs last week that the trail of the alleged cover-up could reach beyond the Whips' Office, to the Cabinet Office and even No 10.
During the questioning of former whip David Willetts last Tuesday, Labour MP Dale Campbell-Savours mentioned that there had been a 1994 meeting between Chief Whip Richard Ryder, Michael Heseltine and John Major about Mr Hamilton, the former Tory minister alleged to have accepted cash for questions from Mohamed al-Fayed, the owner of Harrods.
It was alleged last week that Andrew Mitchell, a government whip, used his privileged position on the former Members' Interests Committee to provide inside information on the Hamilton case to Mr Ryder.
But Angela Eagle, a Labour member of the former Members' Interests Committee, which was supposed to carry out the initial investigation into the into complaints laid against Mr Hamilton, went even further in a weekend interview.
Ms Eagle is now certain to be asked to give evidence on what happened in the committee. She told Channel 4's A Week in Politics that Mr Mitchell had been the primary advocate of not pursuing allegations "which involved Harrods vouchers and alleged envelopes full of cash". "We could make no progress," she said. "We were not allowed to look at the evidence. We were prevented from hearing witnesses ... I felt at the time ... that the whip was the main instigator of these blocking manoeuvres."
A separate investigation is being carried out by Sir Gordon Downey, the Parliamentary Commissioner for Standards, into the allegations about Mr Hamilton opened up following the collapse of his libel action against The Guardian.