The Tory leadership contest is now unofficially underway, with Boris Johnson’s resignation setting the wheels in motion for a new Prime Minister to take the reins.

The beleaguered PM finally made the decision to bow out as support for his premiership collapsed around him, with upwards of 50 MPs quitting government and party posts since Tuesday evening.

He will remain as Prime Minister until a successor is in place, expected to be by the time of the Conservative Party conference in October.

Mr Johnson’s departure fires the starting gun for a contest to replace him.

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The exact timetable for this is agreed by the 1922 Committee and Tory Party HQ, with Conservative MPs and party members playing a decisive role in electing the next leader.

Tory MPs will whittle down the candidates to a final two through a balloting process, with party members then voting on who they would prefer.

In the meantime, Mr Johnson will remain as a caretaker prime minister.

Possible contenders who have not yet announced their candidacy include Rishi Sunak and Sajid Javid, whose resignations from Cabinet on Tuesday triggered the mass exodus that ultimately crippled Mr Johnson’s leadership.

Foreign Secretary Liz Truss has made little secret of her leadership ambitions, with a series of high-profile interventions and photo opportunities in which she appeared to be channelling late PM Margaret Thatcher.

Despite being a fervent Johnson loyalist, she was nowhere to be seen as the Government crumbled around him.

She is now cutting short an official trip to Indonesia and will issue a statement shortly, sources close to her said.

Some Tories have already made their ambitions clear. Attorney General Suella Braverman launched an unlikely leadership bid as support for Mr Johnson crumbled around him on Wednesday night.

Previously a loyalist to the departing PM, she told Peston on ITV that he had handled matters “appallingly” in recent days and that “the balance has tipped now in favour of saying that the Prime Minister – it pains me to say it – but it’s time to go”.

Ms Braverman, who was first elected as an MP in 2015, will be regarded as something of an outsider for the leadership given the party grandees already tipped to be running.

Prominent Brexiteer and former minister Steve Baker, a senior Tory backbencher, also confirmed on Thursday he is seriously considering putting himself forward for the top job.

He told Times Radio people are asking him to do it, and it would be “dismissive and disrespectful” if he did not heed expressions of support, though he said he regards the prospect with “something akin to dread”.