Nick Clegg and two senior Liberal Democrat colleagues failed to take tough enough action to investigate allegations of sexual harassment against Lord Rennard, the party's former chief executive, an investigation has concluded.
The Deputy Prime Minister admitted the report into attitudes towards women in his party made "sobering reading" and promised a drive to eradicate sexism from within Lib Dem ranks.
The inquiry was commissioned by Mr Clegg after several women claimed this year that Lord Rennard had harassed and propositioned them and accused the party of failing to act on their complaints.
The peer, who stood down as chief executive because of ill-health, denies all the accusations.
The investigation, conducted by the prominent businesswoman Helena Morrissey, cleared senior party figures of conspiring to cover up allegations.
But it accused Mr Clegg, Danny Alexander, who is now the Chief Secretary to the Treasury, and Jo Swinson, who is now the Consumer Minister, of blundering by not launching a formal inquiry into the allegations.
Ms Morrissey said: "Mistakes were definitely made. They were made by Nick Clegg, Danny Alexander and Jo Swinson. I think you can make a mistake and learn from them - it's different from setting out to mislead or to do something wrong."
She said of Mr Clegg: "He and others should have asked more questions for the sake of Lord Rennard and everyone else."
Two women approached Ms Swinson, who was chairing the party's gender balance task force at the time, with complaints about Lord Rennard in 2008.
Ms Morrisey's report said she did not keep a formal note of their allegations because they said they wanted to remain anonymous and simply put "sticky notes" in her Filofax to remind her to contact the women again.
Ms Swinson then approached Danny Alexander, who was Mr Clegg's chief of staff, to raise the allegations without naming the women. He then passed the complaints to Mr Clegg and Paul Burstow, who was the party's chief whip. Mr Alexander challenged Lord Rennard, who denied the claims.
The report said: "The issues were 'handled' informally, principally by Jo Swinson and Danny Alexander, because that is what they thought the women wanted - primarily to protect their identities.
"While their actions were, I believe, in good faith, this approach was ultimately not sufficient."
Mr Burstow has apologised for not encouraging the women to make a formal complaint.
Scotland Yard is investigating allegations against the peer and an internal party investigation is on hold pending the outcome of the police inquiry.
Mr Clegg said: "Over a 20 year period a series of mistakes were made which left a number of women feeling seriously let down and for that there is absolutely no excuse whatsoever.
"The report also shows that the individuals who dealt with their complaints had the right motives, but there weren't the right processes in place to support the women who'd come forward. And as Leader of the Liberal Democrats I take responsibility for that."
Ms Morrisey heard 32 complaints of sexual harassment and misconduct in different sections of the party, including one councillor who complained she endured "aggressive, sexist and patronising" behaviour from colleagues.
Mr Morrisey, the chief executive of Newton Investment Management and founder of the 30% Club which campaigns to increase the proportion of women in company boardrooms, said: "There is definitely a mismatch between what the party espouses as its ideology and reported behaviour at local party level."
NHS chief denies gagging cover-up
The head of the NHS in England has denied claims that he staged a "cover-up" over the use of gagging orders to prevent staff speaking out about conditions in hospitals.
Appearing before the Commons Public Accounts Committee, Sir David Nicholson angrily denounced the claims made by Tory committee member Stephen Barclay as "erroneous and wrong".
Prior to the hearing, Mr Barclay said figures obtained under the Freedom of Information Act showed that since 2008 at least 52 staff had been prevented from speaking through the use of confidentiality clauses at a cost of £2m to the taxpayer.
Mr Barclay said that Sir David had either been complicit in a "systemic cover-up" or had failed to ask questions about what was happening in the NHS.
Sir David told the committee: "I can absolutely refute that I have ever been involved in any kind of cover-up in relation to the expenditure that's identified. I have been absolutely honest and truthful."