Conservative MPs will vote in the first round of the party’s leadership contest later today.
All 10 hopefuls have launched their campaigns but it is expected that at least one MP – probably more – will be out of the race by the end of the day.
Each candidate needs at least 17 votes to get through, a threshold introduced as a result of rule changes agreed to by the Conservative Party’s executive.
The changes were designed to expedite the process in the most crowded field of any Tory leadership contest in history.
If each candidate receives 17 votes or more then the one with the fewest MPs backing them will be eliminated, a process that will continue until only two candidates remain.
After hustings around the country, party members will vote in a postal ballot and the new prime minister will be announced in the week of 22 July.
Former foreign secretary Boris Johnson is the favourite among Conservative MPs, a Sky News analysis has found.
Mr Johnson has the support of 80 MPs, well ahead of his nearest challenger Jeremy Hunt, who is on 33.
One of Mr Johnson’s supporters, Theresa Villiers, told Sky News: “This isn’t about selecting a leader of the opposition where you have time to develop them, this is about the prime minister, so the normal rules in the leadership where an unknown comes through will not happen here.
“People know they have to have someone ready-made for the job cos day one, it’s about running the country, so I am confident. The more I see of Boris, the more I’m certain he’s the right man.”
Mr Johnson launched his campaign insisting he was right for the job, despite controversial comments that have included referring to Muslim women wearing the burka as “letter boxes” and “bank robbers”.
“If sometimes in the course of trying to get across what I genuinely think, I use phrases and language that have caused offence, of course I’m sorry for the offence that I have caused,” he told Sky’s political editor, Beth Rigby.
“But I will continue to speak as directly as I can.”
Mr Hunt is also likely to make it through the first stage of the process and supporter Alistair Burt said: “If it’s up to individual qualities and the skills and abilities of candidates to impress colleagues, I’m quite sure Jeremy Hunt will be there.”
Mark Harper, Esther McVey and Rory Stewart are among those expected to struggle in today’s vote.
But Mr Harper said he was “confident” and rival former Commons leader Andrea Leadsom said she was “very optimistic”.
It is the first time a prime minister has been chosen in this way.
It would have happened in the last leadership contest where Theresa May was elected but her closest rival, Mrs Leadsom, withdrew to leave Mrs May unopposed.