Senior Liberal Democrats suggested for the first time on Monday that Lord Rennard had not stood down as the party's chief executive for health reasons, but after pressure from Nick Clegg's office and the then party president over general allegations of sexual impropriety.

The revelation came just hours before the Metropolitan police confirmed they were investigating "whether or not criminal activity has taken place". A Scotland Yard spokesman said: "The Metropolitan police special investigations command has been approached by officials in the Liberal Democrat party and is working with them to ascertain whether or not criminal activity has taken place."

Rennard resigned months after being confronted by Clegg's then chief of staff, Danny Alexander, in December 2008 over allegations of harassment, which he strenuously denies.

Some of the women who had made the complaints were assured by party officials at the time that his departure was linked to the allegations.

A senior party source said: "He left months after his very difficult interview with Danny Alexander, and that was for a reason."

It also emerged that the then party president, Lady Scott, was informed of the allegations during her presidential campaign in late 2008.

Chris White, her election agent for the presidential campaign, said: "What I can say is that Ros Scott was extremely concerned about the allegations but frustrated by the fact that people were understandably reluctant to come forward. Chris Rennard ceased to be chief executive in the first year of her presidency."

The Guardian's source said: "The stories, independently provided, were awful and she resolved to get rid of him."

At the time of Rennard's departure in spring 2009, the party cited health reasons. Rennard is a long-term diabetic. One source said the other option was to hold an internal disciplinary procedure, but the likelihood of Rennard receiving due process given the likely media leaks was minimal.

The revelation came as Clegg's office battled to show he had not been deaf to claims of Rennard's alleged sexual harassment made anonymously by women in the party and alleged to date back to 2004.

Rennard has strenuously denied the allegations, but has accepted he was interviewed by Alexander, although no specific allegations were put to him.

Clegg's chief of staff and then director of communications, Jonny Oates, was also under pressure after it was revealed the Daily Telegraph put specific allegations to him about Rennard at the close of the 2010 general election campaign.

The Telegraph asked whether Clegg was aware of the five specific allegations, but Oates did not pass the inquiry on to Clegg.

The letter was sent four days before polling day and marked private and confidential. It also claimed that the allegations had been passed to Jo Swinson, the party's equalities officer.

Sources close to Oates say he did not pass the claims to Clegg because he was certain from previous conversations with Clegg that the party leader was not aware of any previous specific allegations.

One friend said: "He did not need to put the allegations to him because he knew that Clegg was unaware of any specifics. That was the problem with the anonymous complaints that were made. No one wanted to say anything on the record."

He also checked the one allegation in which an individual witness was named, and the witness denied any knowledge of the incident.

In a brief written response, Oates replied at the time to the Telegraph: "It is untrue to state that Mr Clegg was made aware of the incidents you allege. Given this fact, it is obviously untrue to state that Mr Clegg asked Jo Swinson or anyone else to carry out an investigation into the incidents that you allege."

Oates's friends acknowledge that he should probably have passed the letter to party officials after the election, but by then Rennard had long left his post of chief executive, and Oates became preoccupied with negotiations to form the coalition with the Conservatives.

A Lib Dem spokesman denied a report night that a £50,000 gagging clause banning the party and its former senior fundraiser Helen Jardine-Brown, from discussing the reasons for her departure was linked with the Rennard allegations.

He said: "We are unable to speak about the specifics of this case for the same reason the person involved can't. I can, however, confirm this case had absolutely nothing to do with the recent allegations involving Lord Rennard. It is completely untrue to suggest otherwise."

The Lib Dems have set up two inquiries, the first to examine the allegations into Rennard's behaviour, led by Alistair Webster QC, a former chairman of the Liberal Democrat Lawyers Association, and a second inquiry to be independently chaired into how the Lib Dems handled the complaints against Rennard.

Alison Smith, a Lib Dem activist and one of the women who made the original allegations about Rennard to Channel 4 news, told BBC Newsnight night that there was a wider problem in the party.

"This culture is absolutely intolerable," she said. "It is going beyond the pat on the knee a lot of the time, and even if it was just the pat on the knee, who gets to decide what is an acceptable advance and what is not an acceptable advance? The power dynamics in these situations are quite scary."

Asked what she would say to other women thinking of going to work for the party, she replied: "I would have to ask them, 'Are you sure?' if nothing is done.

"And I would have to tell them exactly what I had come up against and what other people I know came up against. But I am hoping that something will be done.

"I think you can see very slowly things [change] at the top of the party. There are definitely things changing. There is some movement there."

The party president, Tim Farron, has already admitted the party's culpability. "The one thing I probably can tell you without going through due process is that we screwed this up as a party," he told the BBC.

"There are individuals out there who we have a duty of care towards who we did not fulfil that duty of care to them and that is something we have to learn from, apologise for, and make sure never happens again."

Clegg insisted he had nothing to hide, but his tone has shifted from claiming the allegations were indirect and non-specific to asserting they were not very specific. He said: "There are lots and lots of questions but I hope I have given a full, frank, honest account. I have got nothing to hide, the party has nothing to hide. We have now got to listen to the women who feel they weren't properly listened to and get to the truth and that is what we will do."

Party officials acknowledged that rightwing papers were exploiting the party's embarrassment to damage the Lib Dems in the Eastleigh byelection, but accept the complaints pre-dated Eastleigh, and was initially generated by party women angry that Rennard appeared to be returning to the front line of Lib Dem politics, as well as attending gender equality sessions.