Liberal Democrat leader Nick Clegg has said it would not be "appropriate" for Lord Rennard to return to his party's ranks in the House of Lords without first apologising to the women who claim he sexually harassed them, warning the under-fire peer: "No apology, no whip."
Mr Clegg's authority faces a major challenge today, as Lord Rennard plans to take up his place in the Upper House and his legal adviser threatens legal action if the whip is not reinstated.
Lord Rennard strenuously denies the allegations against him and has refused to apologise, after an inquiry by senior barrister Alistair Webster QC found that the women's claims were credible but could not be proved beyond reasonable doubt.
Mr Clegg said that if the whip was restored to the party's former chief executive without any apology, it would be "in defiance" of his authority. And he warned: "Clearly, if it were to happen, matters would not rest there."
The Deputy Prime Minister told ITV1's Daybreak: "What is on the line here is basic decency. When you have caused offence and distress to other people, even if it doesn't end up in the hands of the police or the courts, basic decency suggests you should apologise,
"That is what Lord Rennard has been asked to do after a formal investigation and a process - recommended by an independent QC. I really think he needs to do that.
"I don't think it is appropriate that he should be sitting in the House of Lords if he hasn't provided that apology - no apology, no whip, if you like.
"That is my view, it is the view of many party members and it is the view of the person who did that formal inquiry on the party's behalf. I very much hope that he - and other colleagues of his in the House of Lords - will listen to that and make sure that the apology is issued, so that people who have been subjected to behaviour which did cause them distress at least get that from him."
Liberal Democrat chief whip Lord Newby and the party's leader in the Upper House, Lord Wallace, can decide to withhold the whip from Lord Rennard.
If they do then he would almost certainly appeal, triggering a vote of the party's peers whether to readmit him to the Lib Dem group in the Lords.
Mr Clegg said that if the Lib Dem peers vote to readmit Rennard, "clearly it would be in defiance of basic decency, it would be in defiance of what the independent formal processes have recommended, in defiance of me and in defiance of of the president of the party".
He added: "That is why I hope it will not happen this afternoon. Clearly if it were to happen, matters would not rest there."
A number of Lib Dem members have suggested that Lord Rennard's refusal to apologise brings the party into disrepute, which could trigger a new disciplinary process resulting in the whip being suspended.
The Regional Parties Committee will meet to consider the possibility of fresh disciplinary action in response to the complaints.
But Lord Rennard won the backing of Lib Dem Euro MP Chris Davies, who played down the allegations against the peer and attacked Mr Clegg's handling of the row.
Mr Davies told BBC Radio 4's Westminster Hour: "This isn't Jimmy Savile, it is touching someone's leg six years ago, at a meeting, through clothing.
"This is the equivalent of a few years ago, an Italian man pinching a woman's bottom. How much more must this man be made to suffer through the media condemnation that comes out day after day fed by the party leadership?"
Mr Davies added: "The whole thing has become like the Salem witch trials... A good man has been publicly destroyed through the media with the apparent support of Nick Clegg. It is completely out of proportion, nonsense and outrageous."
Lib Dem peer Lord Carlile, who has been offering legal advice to Lord Rennard, warned during an interview on the Sky News Murnaghan programme that the row could escalate.
He said: "Here, we have a situation in which there has been found to be no case against Lord Rennard but he is being lined up against the wall by people who are trying to force him to apologise in a way no lawyer would advise and in which he should not apologise for all kinds of reasons."
If the whip was removed then "the matter could unfortunately end up in the public law courts", he warned, adding: "Nobody wants that to happen and I don't begin to understand why Nick Clegg has intervened after a process which has been concluded in Lord Rennard's favour".
Mr Clegg told Daybreak there were no grounds for "legal sabre-rattling", because the demand for an apology had not been instituted by him, but was recommended by Mr Webster, who said it was a matter of "common manners".
Mr Webster said : "The suggestion that Lord Rennard might wish to apologise was not one I envisaged as being contentious.
"I viewed Lord Rennard, from the weight of the evidence submitted, as being someone who would wish to apologise to those whom he had made to feel uncomfortable, even if he had done so inadvertently. I would consider it to be common manners."
Former leader Lord Ashdown signalled the irritation felt within the party at Lord Carlile's role.
"I fear he is advising Chris Rennard as a lawyer, but not as a friend," he wrote on Twitter.
Mr Clegg told BBC1's Breakfast programme that Mr Webster had found that "whilst there wasn't enough proof to suggest that, in effect, a criminal offence had been committed, nonetheless there was evidence to show that real distress had been caused to a number of women in the party".
He added: "I have a duty of care not only to those women, I have a duty to ensure that those recommendations of an independent formal process are properly upheld, and I have a duty to say loud and clear as leader of the Liberal Democrats that I expect everybody to treat each other with civility and dignity and respect - particularly people in a position of authority. Where that has not happened, it is quite right, as a minimum, that one simply apologises."
Asked whether his inability simply to impose his will on the party in the Rennard affair exposed flaws in the Liberal Democrats' internal processes, Mr Clegg said: "I admit that some people sometimes think that, because I'm the leader of a political party, I somehow should act as if I'm the leader of a sect. I'm not.
"Of course, leadership is partly about direct powers. Leadership is also a process of persuasion and setting out your views."
Asked about the prospect of legal action by Lord Rennard, Mr Clegg said: "Clearly, I hope and don't believe it will end up in the High Court, because there's just a rather basic principle of decency here at stake, which most people outside politics would think is in many ways - as Alistair Webster, the QC who wrote the report, said yesterday - uncontroversial."