Video report from ITV News Political Correspondent Emily Morgan
The Whitehall inquiry into First Secretary of State Damian Green has been widened to look at allegations that pornographic material was found on one of his parliamentary computers, Home Secretary Amber Rudd has said.
Mr Green, who is effectively Prime Minister Theresa May's deputy, has strongly denied the claims and called them a political smear.
The Sunday Times reported that ex-Scotland Yard assistant commissioner Bob Quick alleged the material was discovered by officers during an inquiry into government leaks in 2008.
The alleged pornographic material found was deemed lawful but one of the investigating officers said some of it was "extreme".
But First Secretary of State Mr Green said the report was "completely untrue" and came from a "tainted and untrustworthy source".
Mr Green is already the subject of an inquiry by the Cabinet Office's Sue Gray after a woman alleged that he made inappropriate advances to her, claims he strenuously denies.
Ms Rudd told BBC One's The Andrew Marr Show: "I know that the Cabinet Office is going to be looking at this tomorrow along with the wider inquiry about Damian, and I do think that we shouldn't rush to allege anything until that inquiry has taken place."
Asked if the Government would collapse if Mr Green was forced to resign, the Home Secretary said: "Absolutely not."
Mr Green said there was a "complete lack of evidence"and the claims "amount to little more than an unscrupulous character assassination" in a statement released on his Twitter page.
It comes amid faced fresh allegations of sexual harassment or inappropriate behaviour from MPs in the Sunday papers in a scandal currently engulfing Parliament.
Conservative MPs Stephen Crabb, Dan Poulter and Daniel Kawczynski also face renewed inquiries over their behaviour.
And Tory whip Chris Pincher has voluntarily stood down and referred himself to police following allegations over his behaviour, a Downing Street spokesman said.
One Tory MP has called for Mr Green to step aside from his ministerial role while he is investigated.
Heidi Allen told Peston on Sunday that if he had nothing to hide then he should make way until any investigation had taken its course.
Meanwhile, the Observer has reported that Sir Michael Fallon’s sudden decision to quit as Defence Secretary was prompted by a second complaint by a journalist.
Jane Merrick, who was then a junior political reporter at the Daily Mail, said she “shrank away in horror” after Mr Fallon tried to kiss her on the lips after a lunch meeting in 2003.
“I felt, humiliated, ashamed,” she wrote of the alleged incident.
She informed Downing Street of the alleged incident on Wednesday, hours before Mr Fallon announced he was stepping down from his post as his behaviour had "fallen below the high standards" required of the armed forces.
The newspaper said the complaint had been the “tipping point for No 10” over the behaviour of Mr Fallon, who had already apologised for repeatedly touching the knee of journalist Julia Hartley-Brewer at a dinner 15 years ago.
The Observer quoted a friend of Mr Fallon who said the MP acknowledged that the latest claims were accurate.
“Michael realises this kind of incident was unacceptable which is why he had to resign,” they said.
Earlier on Sunday, childcare minister Mark McDonald resigned from the Scottish Government over claims of “inappropriate behaviour”.
“I apologise unreservedly to anyone I have upset or who might have found my behaviour inappropriate,” he said in a statement.
Meanwhile, there have been growing calls within Parliament for an independent system for dealing with allegations or sexual harassment or assault.
John McDonnell said there was "clearly" a problem which ran across all the main parties and that action was needed both to protect victims and maintain confidence in Parliament.
The Chairman of the Committee on Standards in Public Life, Lord Bew, has also said outside bodies needed to be involved in harassment investigations to avoid claims of a cover up.
"The parties need to get a grip of this issue of accountability. It's vital that these things are not seen to bed one in-house," he told the BBC.
"It is vital that there are people outside Parliament in cases of harassment, and so on, who are there, who can give some reassurance to the public that this is not just another cover up."