Conservative MPs will vote tonight on whether Theresa May can continue as leader of the party.
At least 48 Tories have submitted letters of no confidence in the PM, with a ballot taking place between 6 and 8pm this evening.
If Mrs May loses, a leadership election will happen immediately.
There is no clear frontrunner to take over from Mrs May, leaving a strong possibility she could win a confidence vote. If this happens another leadership election cannot take place within the next 12 months.
If she loses and an election is triggered, any MP who wishes to run as candidate needs the support of two fellow MPs in order to get onto the ballot paper.
Tory MPs then vote using the first past the post system. If more than three candidates have been nominated, the one with the lowest proportion of votes is eliminated and another ballot is held. This process continues until two candidates remain.
Conservative Party members then vote for the two nominees, and the winner becomes the new leader.
These are the candidates tipped to take over – and their realistic chances of doing so.
The former Brexit Secretary, who resigned in protest against Theresa May’s Brexit deal, has been touted as a possible PM.
His decision to quit over the deal, which is hated by hard Brexiteers, could win him support from the faction who wish to install a Eurosceptic to renegotiate a Brexit deal with the EU.
However he is also viewed by many as shrugging off responsibility for a Brexit deal he himself was tasked with negotiating. This failure as a minister is seen to suggest unsuitability for high office.
The Home Secretary has won support across the board for his performance in his current role, condemning the hostile environment policy and helping to force a U-turn from the Government over visas for highly-skilled migrants.
Javid may have damaged his standing with Brexiteers by campaigning for Remain during the EU referendum campaign, but has since about-turned to become an ardent Brexit supporter.
The former foreign secretary quit the government in July over Theresa May’s handling of Brexit, and has been a regular and vocal critic of her approach ever since, leading the Brexiteer calls to ‘chuck Chequers’.
According to a poll by grassroots organisation ConservativeHome, Mr Johnson is the favourite among party members to take the helm.
However he is an unpopular figure among Tory MPs, and his stint in the Foreign Office was seen as unsuccessful, and even disastrous, by his colleagues. It’s unlikely he could secure enough support from Tory MPs – though not impossible.
Michael Gove is clearly keen for the top job, running against Mrs May in the last leadership race.
He is popular among Eurosceptics and has voiced cautious criticism of the Prime Minister’s Brexit stance.
His stint as Environment Secretary has won him public favour, and his war on plastics has proved popular with voters.
However Mr Gove is considered to have stabbed Boris Johnson in the back during the last leadership election, pulling support for his colleague in order to launch his own bid. The memory of this means a number of MPs still consider him untrustworthy.
A former Remainer turned Brexit cheerleader, Jeremy Hunt is seen as a safe pair of hands among an assortment of loose cannon colleagues.
However he irked Remainers – and the EU – recently by comparing the European Union to to the Soviet Union in a move that damaged his reliable reputation.
He has publicly backed Theresa May a number of times, pledging her his ‘full support’, but could still throw his hat into the ring in the event of an election.
Jacob Rees-Mogg has insisted numerous times that he is not interested in leading his party. But the committed Brexiteer has a solid base of EU-loathing fans who would like him to do so.
The backbencher has never held a ministerial post, and is realistically too divisive to stand much chance of making it onto the ballot paper.
What about the PM herself?
There is no single candidate who enjoys support across the unite the warring Tory party, meaning that the likely winner of a no confidence vote will be Mrs May herself.
If more than half her party backs her she can stay in position, and cannot be challenged again for another year.
Another former Brexit Secretary David Davis is understood to still have his eyes on the hot seat after a failed leadership bid in 2005.
Penny Mourdant, another Brexiteer, could be in with a chance. However she wavered over whether or not to resign over Theresa May’s Brexit deal, and her decision not to do so could mar her popularity with hard Brexit supporters.
Andrea Leadsom, who stood against Mrs May last time around, also has a shot. She is thought to be the ringleader of the cabinet ministers attempting to alter the PM’s Brexit strategy from the inside.