Those wanting to win the keys to Downing Street have until Monday to secure the backing of 100 MPs, and must meet this threshold to make it onto the ballot paper.

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This means there can only be a maximum of three candidates for the top job, and the field will be narrowed to two by MPs before heading to the wider party membership for a vote - unless Conservative politicians unify behind one person.

The latest Sky News tally suggests Mr Sunak has 85 Tory MPs supporting him, while Boris Johnson has 47 and Penny Mordaunt has 19.

But so far, only Ms Mordaunt - the leader of the House of Commons - has actually announced her intention to run.

Last night, Conservative MP Sir James Duddridge confirmed to Sky News that he had spoken to Mr Johnson, who had told him he was "up for it".

Candidates will spend the weekend shoring up support from Conservative colleagues as the deadline looms for nominations - with Mr Johnson flying back from his Caribbean holiday in economy class.

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The timetable of the contest has been sped up to ensure that a winner is finalised within a week.

It was quickly organised after Liz Truss announced her resignation on Thursday following weeks of market turmoil and unrest within her party as a result of the tax-cutting mini-budget announced to Parliament last month.

She fired her Chancellor Kwasi Kwarteng, with his replacement Jeremy Hunt later reversing nearly all her policies.

It was not enough to quell anger among backbenchers, and she became the UK's shortest-serving prime minister with just 44 days in office.

Whoever does get in power will need to decide quickly whether they will go ahead with Mr Hunt's medium-term fiscal plan, which is set to be announced on 31 October.

Sky News