The departure of Matt Hancock as health secretary should be followed by "proper investigations into which rules were broken", the Mayor of London has said.
Mr Hancock sensationally quit on Saturday night amid outrage after he was pictured breaking social distancing rules kissing his aide.
Sadiq Khan told the BBC's Andrew Marr Show on Sunday: "What's important now is for there to be proper investigations into which rules were broken in relation to use of private email, in relation to the appointment of senior staff and also in relation to the social distancing rules."
The mayor welcomed Mr Hancock's successor Sajid Javid to his new role as a fellow son of a bus driver.
He said: "It's always good to see this small club of children of bus drivers doing really, really well and I wish him all the best."
Mr Hancock had apologised when images and video emerged on Friday of him with Gina Coladangelo in his ministerial office on May 6 but pressure grew on him throughout Saturday.
In a letter to Boris Johnson, he said the Government “owe it to people who have sacrificed so much in this pandemic to be honest when we have let them down as I have done by breaching the guidance”.
He added: “The last thing I would want is for my private life to distract attention from the single-minded focus that is leading up out of this crisis.
“I want to reiterate my apology for breaking the guidance, and apologise to my family and loved ones for putting them through this. I also need to be with my children at this time.”
Mrs Coladangelo–married to millionaire Oliver Tress, founder of retail chain Oliver Bonas–also reportedly resigned her Department of Health role.
Former Chancellor and Home Secretary Sajid Javid will replace Mr Hancock as Health Secretary, Downing Street announced.
In a video posted on Twitter, Mr Hancock said: “I understand the enormous sacrifices that everybody in this country has made, you have made. And those of us who make these rules have got to stick by them and that’s why I’ve got to resign.
“I want to thank people for their incredible sacrifices and what they’ve done. Everybody working in the NHS, across social care, everyone involved in the vaccine programme and frankly everybody in this country who has risen to the challenges that we’ve seen over this past 18 months.”
In response, the Prime Minister wrote to Mr Hancock: “You should leave office very proud of what you have achieved – not just in tackling the pandemic, but even before Covid-19 struck us.”
Mr Johnson had refused to sack Mr Hancock, with his spokesman saying the PM considered the matter closed after receiving the West Suffolk MP’s apology.
Three Tory MPs had broken ranks on Saturday to demand that he resign after The Sun first reported he was having an extramarital affair.
Lawyers described how Mr Hancock may have broken the law regarding coronavirus restrictions, although he admitted only to breaching guidance.
There were also questions about Mrs Coladangelo’s appointment to her role in the Department of Health and Social Care (DHSC) in the first place.
Labour leader Sir Keir Starmer tweeted: “Matt Hancock is right to resign. But Boris Johnson should have sacked him.”
Liberal Democrats leader Sir Ed Davey tweeted: “Matt Hancock’s legacy as Health Secretary will be one of cronyism and failure.
“And the fact that Boris Johnson thought Hancock could just carry on regardless brings the Prime Minister’s judgement into question once again.”
Before he resigned, Tory Duncan Baker said told his local newspaper, the Eastern Daily Press: “In my view people in high public office and great positions of responsibility should act with the appropriate morals and ethics that come with that role.
“Matt Hancock, on a number of measures, has fallen short of that. As an MP who is a devoted family man, married for 12 years with a wonderful wife and children, standards and integrity matter to me.
“I will not in any shape condone this behaviour and I have in the strongest possible terms told the Government what I think.”
Veteran Tory MP Sir Christopher Chope said his constituents were “seething”.
The MP for Christchurch told BBC Radio 4’s PM programme that the annual general meeting of his local party association had “unanimously called on Matt Hancock to resign immediately” and he said he felt this reflected the mood of the public.
He said: “They felt that he was in breach of the ministerial code; that he was in breach of the lockdown regulations; that he is the person who has been passing the laws, signing off the regulations, requiring people to comply with restrictions upon their freedom – many of which people don’t agree with – but they’ve complied with out of respect for the rule of law.
“And they’re absolutely seething now, that having made sacrifices themselves, including not seeing loved ones and all the rest of it, they find that the person who was in charge of all this feels free to not comply with his own regulations and I think that’s the essence of it really.”
Former Cabinet minister Esther McVey, the MP for Tatton, told GB News: “If it would have been me, I would have resigned myself, and I said that for Dominic (Cummings), and I’m hoping that Matt Hancock is thinking the same thing, that he doesn’t have to have it pushed upon him.”
She said it would be “viewed far more admirably” if he resigned.
Conservative MP William Wragg tweeted: “Re Mr Hancock, a thought: Covid regulations have created a dystopian world of denunciation, finger-wagging & hypocrisy.
“Let us be freed from this tyranny of diktat and arbitrary rule. As we shall inevitably see with this sad example, the revolution always consumes its own.”
It comes as a snap poll by Savanta ComRes, released hours after photographs of the pair kissing in Mr Hancock’s ministerial office surfaced, found 58 per cent of UK adults feel he should resign, compared to 25 per cent who say he should not.
The Covid-19 Bereaved Families For Justice group, which represents those who have lost loved ones to the pandemic, also called for Mr Hancock to go.
In a letter to the Prime Minister, the group said it has broken its “position of neutrality on ministerial conduct” to urge Mr Johnson to relieve Mr Hancock of his job.
Ms Coladangelo, a friend from Mr Hancock’s days at Oxford University, was brought into DHSC as an unpaid adviser last year before being given the £15,000-a-year role of non-executive director in the department.
Legislation in place at the time said that “no person may participate in a gathering” that “consists of two or more people… and takes place indoors”.
An exception to this rule was that the gathering was “reasonably necessary for work purposes or for the provision of voluntary or charitable services”.
Tory MPs and ministers will also have been eyeing the by-election in Batley and Spen next week.
Christchurch MP Sir Christopher told the BBC the impact on the West Yorkshire vote was on his mind.
Labour MP for Halifax, Holly Lynch, had been preparing to write an open letter to Conservative MPs and the Tory candidate in the election, Ryan Stephenson, challenging them to tell Mr Hancock to resign.
Before he did, Sir Christopher told Radio 4’s PM programme: “Of course I feel that. And that’s another reason why I think that the sooner he goes the better, because otherwise the last few days of the campaign are going to be dominated by this issue and it’s obviously not going to be very helpful for the Conservatives.”