Norhants MP Leadsom has the '˜zap, drive and determination to be PM' says Boris Johnson

Johnson, who led the campaign to leave the EU and stood alongside Mrs Leadsom during the ITV referendum debate, said the 53-year-old former city banker was his choice for leader in a Facebook post last night.

He said Mrs Leadsom had the “zap, the drive, and the determination essential for the next leader of this country.”

And he added: “She has long championed the needs of the most vulnerable in our society. She has a better understanding of finance than almost anyone else in Parliament. She has considerable experience of government.

“She is level headed, kind, trustworthy approachable and the possessor of a good sense of humour.”

Mr Johnson went on to say Leadsom would be “best placed to help forge a great post Brexit future for Britain and Europe” and had the qualities to “bring together leavers and remainers” over the coming weeks.

The Conservative Party’s 330 MPs will vote in the first round of the leadership election between 11am and 6pm today, with the results expected at about 7pm.

At that point, the poorest-performing candidate will be eliminated from the race.

Further rounds will take place on Thursday and the following Tuesday until two candidates remain, although some may drop out before next week.

Last night Andrea Leadsom garnered mixed reviews when she pitched for her leadership at a Parliamentary hustings in front of MPs.

One MP reportedly told the Sun newspaper the mother-of-three went down “like a cup of cold sick.”

This morning Education Secretary Nicky Morgan backed rival Theresa May, suggesting Leadsom was too “inexperienced” to succeed the Prime Minister.

So far it is understood Mrs Leadsom has the support of around 40 MPs, including former party leader Iain Duncan Smith, and is expected to be in the final two next week.