Who are Oxfordshire's Conservative MPs backing for PM now?

Mr Courts is the only one of Oxfordshire’s four Conservative MPs to switch allegiances after the battle was whittled down to two candidates.

Wantage MP Ed Vaizey and Banbury’s Victoria Prentis are supporting neither the front runner, former foreign secretary Mr Johnson, or his successor Jeremy Hunt, after initially throwing their weight behind other candidates.

John Howell, who succeeded Mr Johnson as Henley's MP, has supported Mr Hunt from the outset.

Around 160,000 Tory party members will now choose which of the men leads their party and the country, after MPs eliminated eight other candidates.

Mr Courts, who resigned from government over Brexit, switched from backing former Brexit Secretary Dominic Raab to Mr Johnson.

He explained: “Boris Johnson is the only candidate who has drawn support from all sides of the Party and is best placed to pursue the One Nation, outward-looking agenda that can unite our country.

“Boris has the ability to revitalise government, has a strong record of delivering in office, and inspires the optimism needed to take our country forward at this critical time.”

In recent tweets praising the rival candidate, Mr Howell urged members to look beyond how people voted in the referendum and suggested doing so was "senseless and destroys any chance for unanimity.”

Mr Vaizey had originally supported Environment Secretary Michael Gove, while Ms Prentis plumped for International Development Secretary, Rory Stewart.

Ms Prentis, who recently met Mr Johnson in a Banbury café, is now remaining neutral.

She explained: “Having played a very full role in Rory Stewart’s campaign, I’m not now declaring for either candidate and it is up to party members.

"There are pros and cons to both.”

Mr Vaizey did not elaborate when asked why he is taking the same position.