Nick Clegg has denied the Liberal Democrats are in crisis but conceded they had "let people down" as he kicked off a potentially fraught party conference.
The Deputy Prime Minister warned activists they had to take a "long, hard look in the mirror" after a number of women raised allegations of sexual harassment.
The sombre message came as senior figures faced fresh questions about another damaging controversy - the conviction of former Cabinet minister Chris Huhne and his ex-wife for swapping speeding points.
In emails disclosed during the case, economist Vicky Pryce suggested she had told Business Secretary Vince Cable, his wife Rachel and Mr Clegg's wife Miriam about the crime well before the claims emerged in newspapers. All three have denied knowing of the swap.
The furore threatened to derail the leadership's hopes of using the spring gathering in Brighton this weekend to build on victory in the Eastleigh by-election. The triumph came despite fears that allegations of inappropriate behaviour by the party's ex-chief executive Lord Rennard - which he has strongly denied - could harm its chances.
Another potential conference flashpoint was defused earlier this week when Lib Dem health minister Norman Lamb announced that widely criticised new regulations on competition in the NHS were being withdrawn. However, there are still likely to be showdowns with activists over so-called secret courts legislation and welfare cuts. Labour has also challenged Mr Clegg to break coalition ranks by supporting the introduction of a mansion tax - long favoured by Lib Dems - in a Commons vote next week.
Lib Dem president Tim Farron cautioned on Thursday night that the party was in a "critical state" and should not assume it had a right to survive. Arriving at conference, Mr Clegg denied the party was in crisis. "No, not at all," he said. "We are in good spirits."
Mr Clegg later took the unusual step of coming on stage at the beginning of the traditional rally event. Reminding activists that it was International Women's Day, he said it was "right that - following the events of recent weeks - we take a long, hard look in the mirror".
"No doubt you will be aware of the recent allegations that have been made about sexual harassment in our party," he said. "I won't talk about the specific allegations. They will be investigated thoroughly and independently and we must respect due process. And we must remember that due process is for the accused as well as the accusers. But I do want to talk about the other side of this. The fact that the women involved feel let down. They deserved to have their concerns and allegations examined thoroughly and properly dealt with. But clearly, that has not always been the case.
"When concerns were brought to the attention of members of my team we acted to address them. But this should not have just been the responsibility of a few individuals acting with the best of intentions. It must be the responsibility of the party as a whole to make sure we have the processes and support structures in place now and in the future. We didn't, and as a result we let people down. Liberal Democrats, that is not acceptable to me. For a party that cherishes equality and women's rights, we have no excuse for failing to live up to the highest standards in the treatment of women. The standards we - rightly - expect of others."