Nick Clegg is facing questions over what he knew about strongly-denied allegations of inappropriate behaviour towards women by a senior Liberal Democrat.
Aides to the Deputy Prime Minister insist he only learned of a series of complaints against the party's former chief executive Lord Rennard when Channel 4 News uncovered details this week.
But the Mail on Sunday published a Facebook discussion of the claims from from January 2009 in which one party worker wrote: "I just don't know how nick can know and not do anything."
The development came as current Lib Dem chief executive Tim Gordon admitted it appeared the party "did not fully live up to our political ideals" in dealing with complaints about the peer.
Lord Rennard - a key party strategist and adviser to a succession of Lib Dem leaders before standing down due to ill health in 2009 - has said he is "deeply shocked" by the allegations, which he "strongly disputes" and regards as a "total distortion" of his character.
Channel 4 News reported on Thursday that two women had claimed Lord Rennard touched them inappropriately. One of them, Alison Smith, a Lib Dem activist who is now a lecturer at Oxford University, said she had spoken to both the then Lib Dem chief whip Paul Burstow and the party's spokeswoman for women and equality, Jo Swinson, about her claims, but claimed no action was taken. A fresh report by the programme on Friday said more women had come forward with similar stories.
The Lib Dems have launched an internal investigation into the "specific allegations" against Lord Rennard under the party's disciplinary procedures. Party president Tim Farron is also conducting a review into the way the party dealt with such allegations.
Mr Clegg has been on holiday on Spain since the story broke, but is likely to face cameras to give his response.
Responding to the initial Channel 4 News allegations, a spokesman for Lord Rennard said: "He regards the report as a total distortion of his character. Not a single complaint of misconduct was made against him to his knowledge during the 27 years he worked for the Liberal Democrat party. Despite the claim made by one woman in the report, Lord Rennard continued working closely with her for ten years after the alleged event described.
"Until this matter is resolved he will withdraw from the Federal Policy Committee on which he serves and temporarily stand aside from the Liberal Democrat group in the House of Lords to seek to avoid any embarrassment to the party. He will remain a member of the Liberal Democrats and will continue to devote himself to good causes through his work in the House of Lords and elsewhere."