Sir Michael Fallon was forced to quit after Cabinet colleague Andrea Leadsom complained about his behaviour, it has emerged.

Tory sources said Mrs Leadsom, the Leader of the Commons, complained directly to Theresa May about ‘vile’ language used by Sir Michael towards her at a parliamentary meeting six years ago.

The former Defence Secretary is said to have told Mrs Leadsom, who had complained of cold hands: ‘I know where you can put them to warm them up.’

Sir Michael is alleged to have been ‘tactile’ and put his arm around Mrs Leadsom in what a source described as ‘unwanted attention’.

However there was a backlash against Mrs Leadsom who was accused of speaking out to further her own career. One senior Tory raged: 'What the f*** does Leadsom think she is doing?'

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Sir Michael Fallon (shown on Wednesday, left) was forced to quit following a complaint from Cabinet colleague Andrea Leadsom (right) about his behaviour towards her, it emerged

The former Defence Secretary (left, in a photo from March) is said to have told Mrs Leadsom (right), who had complained of cold hands: ‘I know where you can put them to warm them up'

Sir Michael is also said to have made derogatory comments of a sexual nature about other MPs on the committee, as well as members of the public who had attended meetings.

A source close to Sir Michael said: ‘He categorically denies saying something as appalling as he knows where she could warm her hands.’

The revelations came as:

Labour MP Kelvin Hopkins was suspended following claims he sent inappropriate text messages to a 24-year-old activist;

Commons Speaker John Bercow called on party leaders to produce plans to tackle sexual harrassment;

Scottish Tory leader Ruth Davidson called on Mrs May to ‘clear the stables’ at the top of the party.

Mrs Leadsom’s complaint is said to be central to the Prime Minister’s decision on Wednesday night that Sir Michael should resign.

The sensational revelation that one Cabinet minister asked Mrs May to sack another will fuel fears that the Westminster sex scandal could tear the Government apart.

Sir Michael is alleged to have been ‘tactile’ and put his arm around Mrs Leadsom (shown leaving Downing Street on Tuesday) in what a source described as ‘unwanted attention’

Sir Michael Fallon sensationally resigned as defence secretary (right with his wife Wendy) yesterday, before revelations about his conduct around Mrs Leadsom (left) surfaced

This is the letter Sir Michael Fallon sent to the Prime Minister announcing his resignation

The Prime Minister said she appreciated the 'characteristically serious manner' in which he had considered his position

Mrs Leadsom made the allegation to Mrs May on Monday. Hours later, with the PM sat beside her in the Commons, she told MPs that ministers should face the sack if they were found guilty of behaviour that made women ‘feel uncomfortable’.

Her intervention sparked a series of crisis meetings in which Mrs May, chief whip Gavin Williamson and Downing Street chief of staff Gavin Barwell tried to establish the truth and agree a way forward with Mrs Leadsom and Sir Michael.

Mrs Leadsom’s complaint is said to focus on comments made by Sir Michael at meetings of the Commons Treasury select committee.

He is said to have made ‘vile’ and ‘inappropriate’ personal remarks to her as well as sexist remarks about other women.

Mrs Leadsom declined to comment. Downing Street also refused to comment on the claims.

Defence sources acknowledged that Sir Michael had made sexist references about other women’s looks in Mrs Leadsom’s hearing, but denied he made the specific remark attributed to him.

But last night senior Tories were said to be furious at Mrs Leadsom for speaking out, accuising her of trying to further her own career.

One source close to Sir Michael asked: 'If you're offended by something, why wait six years to say it? Is this her way of securing political survival?'

And a Cabinet ally of Sir Michael fumed: 'He made mistakes in the past but what the f*** does Leadsom think she is doing? We're supposed to be a team. Does she want to bring down the whole f***ing Government?'

Sir Michael, entering Downing Street yesterday morning hours before he resigned from his position

The MP for Sevenoaks is pictured during Prime Minister's Questions yesterday, sitting on the front bench for the final time

The deal brokered by Mrs May and Mr Williamson was supposed to remain a closely guarded secret to prevent it destabilising the Government. But several sources confirmed details of Mrs Leadsom’s complaint.

Sir Michael admitted on Monday evening that he had touched the knee of journalist Julia Hartley-Brewer at a boozy dinner at the 2002 Tory party conference.

Miss Hartley-Brewer said she had not regarded the incident as ‘anything but mildly amusing’.

Former Tory minister Anna Soubry yesterday said anyone with a brain knew that ‘Kneegate’ was not the reason for Sir Michael’s resignation.

Former Tory leader Iain Duncan Smith also urged Mrs May to get tough with any politicians whose personal conduct threatened the reputation of the Government, saying she needed to ‘rule with a rod of iron’ to prevent the scandal spiralling out of control.

He said: ‘I’m told reliably that Theresa May really does see this as a change moment and she wants to make sure of this.

‘It is critical for Theresa May to rule this thing with a rod of iron over where we are right now. She has to give the lead on this now and say we won’t tolerate this, nobody else should tolerate it.

Defence sources tonight said Sir Michael had told the Prime Minister (pictured together in the Commons) he could not 'guarantee there wouldn't be more incidents like Julia Hartley-Brewer'

‘This is time for us to say in any institution this kind of abuse of power cannot in future be tolerated.’

Speaking after a meeting with Mrs May, Miss Davidson said a clearout ‘is going to (happen) and needs to happen in the next few weeks, months and years’.

She added that the PM was going to need ‘some pretty big shovels for the Augean Stable’ – a reference to the mythical task set for ancient Greek hero Hercules.

But some Tories believe they could face a witch-hunt in which relatively minor indiscretions lead to career-ending sanctions.

Boris Johnson was cornered by the BBC yesterday and asked whether his personal conduct had always met the standard expected of Cabinet ministers. He said: ‘You bet.’

Transport Secretary Chris Grayling urged caution, saying: ‘This is not about clearing out stables.’

Mr Grayling said the departure of Sir Michael was ‘a great shame’ but said the priority now was to introduce procedures to make it easier for victims of sexual harassment and bullying in politics to come forward.