Nick Clegg has conceded that his party made "very serious mistakes" in failing to deal properly with complaints of sexual harassment against its then chief executive Lord Rennard.
The Deputy Prime Minister continued to insist that he was personally unaware of any specific allegations by women in the party until they were broadcast by Channel 4 last week.
But he suggested the issue was "in the background" when the peer - who strenuously denies the alleged inappropriate behaviour - retired from his senior role on grounds of ill-health.
"There were some very serious mistakes and the women were not listened to and were let down," Mr Clegg said as he was grilled on the controversy during his weekly phone-in on LBC 97.3 radio.
"I so much believe that it is crucial that you treat people with respect and dignity in everything you do - and that is what I expect of people in the organisation I lead. That, clearly, did not happen here, to put it mildly."
Mr Clegg said an email sent to a senior aide by the Daily Telegraph shortly before the 2010 election setting out detailed allegations "was not passed on to me". And he insisted that a face-to-face conversation with then MP Sandra Gidley soon after he became leader in 2007 had been "of a general nature".
Pressed on whether the issue played any part in Lord Rennard's departure as chief executive, Mr Clegg said: "Like any new leader of any organisation or political party, I wanted to make sure that the organisation reflected my priorities, my values. I felt it was time for a change at the top of the professional party. His health was poor and that was the immediate reason he left but of course these things were in the background."
The Deputy Prime Minister has been under sustained pressure to explain what exactly he knew about the claims and what he did about them. An initial response from the party asserted that he was not aware of the issue but was later clarified to admit he was aware of general concerns. Lib Dem president Tim Farron has said the party "screwed up" the handling of the complaints - which have sparked two internal inquiries.
Campaigning on Wednesday night in the Eastleigh by-election, Mr Clegg denied that his admission that concerns about Lord Rennard's conduct had been a "background" issue at the time of his resignation amounted to another shift in his position.
He said: "I don't think it is actually an elaboration on what I have been saying for days now, which is that there were general concerns back in 2008 and into 2009, and Lord Rennard stood down in the spring of 2009."