BORIS Johnson’s time as Prime Minister has been characterised by scandal and crisis – from wallpapergate and partygate to by-election losses and a vote of confidence.

In the end, the trigger for Tory MPs abandoning him in droves was the row over Number 10’s handling of the scandal involving former deputy chief whip Chris Pincher.

The resignation of more than 50 ministers and aides, started by former health secretary Sajid Javid and ex-chancellor Rishi Sunak, has brought about the downfall of a Prime Minister once dubbed the “greased piglet” due to his ability to survive various tricky situations.

Questions remain as to why the Pincher scandal was the tipping point for Johnson after his botched attempt to save former minister Owen Paterson from parliamentary suspension, revelations of Downing Street parties during lockdown and becoming the first leader to be fined for breaking the law after being “ambushed” by cake.

His premiership began to unravel with Pincher’s dramatic resignation on June 30 over allegedly assaulting two fellow guests the evening before at the Carlton Club, a Tory private members’ club in London.

Downing Street initially denied the Prime Minister was aware of any “specific allegations” about Pincher when he was appointed to the whips’ office, but Johnson was forced to make a humiliating apology after it emerged he had forgotten about being told of previous allegations of “inappropriate” conduct.

One explanation for why this led to his MPs abandoning him was offered by Tory MP David Simmonds, who represents Ruislip, Northwood and Pinner.

“I think people have looked at the series of decisions made and in particular the most recent one in respect of someone who was the subject of an investigation that found there were allegations upheld, and then we did not get an honest answer and honest account of what the Prime Minister knew about it,” he told BBC Radio 5 Live.

“I think many colleagues after that said enough was enough – if that was a chief executive of a business, if that was a manager in a company who had done that, that is something people would have said was unacceptable.”

When challenged over scandals happening for months Simmonds replied: “Personally my threshold was crossed with partygate, but others need to balance do they feel it is better to carry on and seek to do the most good you can, or is it better to draw a line under it and say no actually I am just going to step away from this and demand that change happen.”

However, Darren Lilleker, professor of political communication at Bournemouth University, said anger at the continual scandals was likely to have been a factor – but not the only one.

He said: “I feel that the situation in the Cabinet, and the party, have been pretty chaotic for some time.

“For the last eight or nine months, ministers have been going on record repeating the official line from Boris Johnson, only to find the line being changed or the claim from Johnson being proven inaccurate.

“I feel they had had enough and saw this as damaging not only to Johnson but also to the Government and party as a whole, as well as to the individual ministers.”

He added: “I also get the sense some ministers were concerned that Johnson wanted to push for more public spending in order to buy off voters annoyed over the scandals, spending they felt was unsustainable long term and counter to Conservative values.

“These two factors came together at this moment and the senior party members decided they have had enough.”

The race to the new leader of the Conservative Party is now under way, with Sunak the most high-profile figure to announce his candidacy so far.

Johnson has said he will remain in post until his replacement has been elected, but faces a growing revolt over suggestions he may cling on until as late as autumn, meaning he would have unprecedented months in office, despite having announced his intention to resign.

Lilleker said: “I feel he should have resigned with immediate effect.

“He does not have the support of enough members of his own party to remain as leader and for the good of the party a clean break is needed.

“I also feel for the good of the country it is unwise to have a narcissistic leader in charge who has nothing to lose.

“He will try to leave a legacy and that could have negative longer-term consequences.”

There’s also the question of who will replace him – and whether the party will make a strategic move to select a Prime Minister distanced from Johnson who may be more acceptable to the public, or choose their new leader based on ideology. MPs will vote to whittle down the candidates to two, with the winner decided by a ballot of party members.

The timetable for this is expected to be set out after a meeting of the 1922 Committee of Tory backbenchers tomorrow.

Lilleker said the big issue for any new leader would be the domestic economic situation.

“Johnson seemed to want to spend heavily to win public support,” he said.

“But this is not the Conservative way. So it is likely that a PM who is not trying to win the public over after becoming embroiled in a scandal might take a longer term view and limit public spending – but again that depends on the individuals.”