The Conservative Party wants a new leader installed by September 5, which means the process must get a move on.

And it will.

Six o'clock on Tuesday evening July 12 is the deadline for candidates to declare themselves in the race and confirm they have the support of at least 20 fellow MPs.

On Wednesday the voting begins. Each candidate coming in with less than 30 votes from colleagues will be out.

It's an algorithm designed to produce a two-horse race by the middle of next week, when MPs will hand it all over to the 160,000 Tory party membership, giving them the summer to make their choice by postal vote.

Lines are already being drawn. The favourite in the parliamentary party appears to be former Chancellor (finance minister) Rishi Sunak.

Launching his campaign, Sunak pledged a considered approach to the economy and distanced himself from what he called economic "fairy tales."

He described a long-term approach where he would "tackle inflation, grow the economy and cut taxes."

In contrast to Sunak's centrist messaging, there has been a flurry of promised tax cuts from candidates to the right of the party, promises dismissed publicly as "populist nonsense" by1990s Conservative Chancellor Kenneth Clarke.

Former equalities Minister Kemi Badenoch, a surprise low-profile candidate, said politicians have been telling people for too long that "you can have your cake and eat it."

"I'm here to tell you that isn't true," she said.

There are other candidates from the right, pro-Brexit and pro-small government, like Penny Mordaunt and Foreign Secretary Liz Truss.

Truss, who campaigned against Brexit in the UK's 2016 referendum but has since become a fully-fledged supporter, has powerful backing within the parliamentary party but, like Rishi Sunak, is less popular with the Tory membership.

The Labour Party is now calling for a vote of no confidence in Boris Johnson, which is likely to happen in parliament on Wednesday.

Number 10's plan was for Johnson to stay in office as caretaker PM until September. A parliamentary vote against him would disrupt that process and it's likely the Tories will see it off with their majority in the House.

In all, the field currently stands at ten candidates. Transport secretary Grant Shapps has already dropped out and joined Justice secretary Dominic Raab in supporting Sunak.

Conservative leadership races can be brutal, they can also be riddled with backstage deals and public surprises.

This one is unlikely to be any different.