British Conservative MPs – the most duplicitous electorate in the world, it is often said – begin the process of whittling down contenders to lead the party and, probably, the country on Thursday.

The party's 313 MPs will each throw a vote behind one of 10 candidates in the first round of an election which history suggests will be highly tactical and is likely to throw up a surprise.

The election is, on the surface, about having a new leader tackle Brexit and setting a fresh direction for Britain, but for those voting, it is also about their personal futures. Back the right candidate and their career path becomes much brighter.

Former foreign secretary Boris Johnson begins the campaign as the frontrunner. He has the most declared support among MPs (79, according to grassroots blog ConservativeHome), and YouGov polling suggests he is the clear favorite of the Conservative members, who will make the final decision. 

But history reveals a repeated truth of Conservative leadership elections: The early frontrunner doesn't win.

Back in 1975, Margaret Thatcher ousted incumbent leader Edward Heath; in 1990, Michael Heseltine challenged Thatcher only to lose out to compromise candidate John Major; in 1997, William Hague defeated a parade of established figures; in 2005, a little-known David Cameron defeated favorite David Davis.

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And in 2016, Johnson himself began as the frontrunner in the wake of the Brexit referendum only for his bid to implode when his campaign manager Michael Gove quit to launch his own challenge, saying the former London mayor wasn't up to the job. 

Ultimately Theresa May was crowned prime minister after her last remaining rival, Andrea Leadsom, pulled out amid controversy over her claim that being a mother made her a better choice to lead the country.

Why does the frontrunner tend to fall? Being the leading candidate means intense media scrutiny – one of the reasons Johnson has so far put himself forward for no live media interviews, while other contenders have grabbed any available microphone – and puts him or her in the firing line of other contenders.

The leaders of the chasing pack are current Foreign Secretary Jeremy Hunt (37 MPs) and current Environment Secretary Gove (34 MPs), followed by former Brexit secretary Dominic Raab (23 MPs), Home Secretary Sajid Javid (19 MPs), and Health Secretary Matt Hancock (16 MPs). 

The remaining candidates – Andrea Leadsom, Mark Harper, Rory Stewart and Esther McVey – are struggling to win the support of the 17 MPs required to progress to round two.

But there are several important factors to remember. 

Firstly, around a quarter of MPs have not committed to any candidate.

Secondly, the duplicitous reputation of the MPs in leadership contests is not for nothing – it's a secret ballot, and what they say in public may not be what they do in private.

Thirdly, Thursday is only the first round of voting and the field is unusually crowded. At least one of the candidates will drop out and bring their supporters to other camps ahead of the second round on June 18. 

The first round is likely to give a better idea of where the race to be Britain's next prime minister lies, but won't be decisive – much can change before the final two candidates are sent to the Conservative membership to pick a winner.

Any contender who proceeds to round two will believe there's a chance of victory. Conservative leadership races always have twists and turns, and tend to end up with a surprise.