Britons could be hours away from discovering who our next prime minister is.
Former PM Boris Johnson pulled out of the leadership race on Sunday, claiming he had the nominations needed to make it onto the ballot paper, but could not unite the Tory party.
His withdrawal means the contest could be decided by early afternoon on Monday unless both the remaining candidates, Rishi Sunak and Penny Mordaunt, can get the support of 100 MPs.
Here are the key timings to look out for on Monday:
By a 2pm deadline, candidates to replace Liz Truss will need at least 100 nominations from Conservative MPs. Those who don't meet the threshold will leave the race.
Nominations can be accepted either by email or signature.
So far, Rishi Sunak has more than 140 public backers, and rival Penny Mordaunt trails far behind him. However, Boris Johnson's decision not to contest the leadership has led to some MPs switching their allegiances.
If both candidates remain in the leadership race, they will participate in a hustings in Parliament.
During the private event, Mr Sunak and Ms Mordaunt will campaign in front of MPs.
6.30pm - 8.30pm
MPs will hold an “indicative” vote. The hope, perhaps, is that the loser of the “indicative” vote may drop out of the race, in which case a new leader emerges without the involvement of Tory party members.
In 2016, When David Cameron quit as PM, the leadership contest did not go to a vote of party members as Theresa May was left unopposed following Andrea Leadsom’s withdrawal from the race. If neither Mr Sunak or Ms Mordaunt drops out, this final vote by MPs will allow Tory members to know – which they did not in the last election – the preferred of the two candidates of the parliamentary party, potentially dissuading them from choosing the other.
The result of the MPs vote will be announced at 9pm.
An online vote will be held for Tory members if two candidates make it through the parliamentary stages by the Monday deadline.
Sir Graham added that "all outreach efforts will be made" for members without internet access.
Results from an "indicative vote" among MPs after two candidates remain will be released for Tory members, in order to get an indication of the mood among Tory MPs. This change to the procedure was not included in the previous contest.
Chair of the 1922 Committee Sir Graham Brady and Tory party chairman Jake Berry announces the process for the upcoming Tory leadership contest.
One television event will be held after Monday so party members and the wider public can hear from the leadership candidates.
It is hoped the entire process will be concluded by next Friday, with Sir Graham saying he expects the new leader to be in place by then.
The leadership contest follows Liz Truss's resignation as prime minister on Wednesday, after just 44 days in office. Her announcement makes her Britain's shortest-reigning prime minister.
Tory party chairman Jake Berry said the board of the Conservative Party met at 4pm and, in conjunction with the 1922 Committee, had decided on the process.
The bar for nominations has risen since the previous leadership contest, where only 20 nominations were needed from Conservative MPs.
Robert Peston sums up an extraordinary 45 days in 45 seconds
While Brady said the threshold is "high", he told ITV News Deputy Political Editor Anushka Asthana that it "should be achievable by any serious candidate who has any realistic prospect of going through".
Former chancellor Mr Sunak, who was runner-up to Ms Truss in the last Tory leadership election, already widened his lead on Sunday night, before Mr Johnson opted not to contest the race.
There is concern from some MPs and security analysts that the election's rapid electronic voting brings risk of hackers skewing the poll.
Mr Berry said he was confident the voting system will be secure.
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