Next Conservative leader: Former campaign manager 'hasn't decided' whether to back Boris Johnson

It comes as Brexit minister James Cleverly becomes first person to pull out of the leadership race

Boris Johnson's former campaign manager "hasn't decided yet" whether to support him in the Tory leadership race, in a blow to the Brexiteer's hopes.

Mr Johnson has pulled ahead of his rivals in the 12-strong race with endorsements from more than 40 Conservative MPs, including key figures in the moderate wing of the party.

But security minister Ben Wallace, who ran Mr Johnson's 2016 bid, would not confirm whether he would support Mr Johnson in the upcoming contest.

In a further blow to Mr Johnson, cabinet Brexiteer Liam Fox announced he would support Jeremy Hunt, who recently described a no-deal Brexit as "political suicide".

It comes as Brexit minister James Cleverly became the first person to pull out of the leadership race, admitting it was "highly unlikely" that he would win.

Mr Wallace, who once joked that he would inflict Game of Thrones-style torture on Michael Gove for stabbing Mr Johnson in the back, declined to say who he would support in the race.

He told BBC Radio 4's Today programme: "I haven't made a decision yet.

"The one thing I have learned from being inside a campaign is we've got another 10 days - your listeners will be dead bored.

"What we do need to do is make sure this race is about getting the right person to lead the country, but I'm not going to bang on about it."

Meanwhile, international trade secretary Dr Fox announced he is backing Mr Hunt as he wants to avoid a no-deal Brexit.

Although he said the UK had to be "willing to walk away", he warned a no-deal Brexit could be used by independence campaigners in Northern Ireland and Scotland.

Asked about the next Tory leader, Dr Fox said: "In this contest I'll be backing my friend Jeremy Hunt, who is an impressive foreign secretary, who is an entrepreneur by background where deal-making is part of his DNA.

"I think he understands we have to message to Europe that we will leave if we cannot get an appropriate deal but we will try to get a deal."

Meanwhile, Mr Cleverly became the first candidate to drop out of the race to succeed Theresa May, which begins in earnest next week.

He said he had asked MPs to "make a leap of faith, skip a generation and vote for a relatively new MP".

Mr Cleverly added: "It is clear that despite much support, particularly from our party’s grassroots, MPs weren't comfortable with such a move and it has become clear that it is highly unlikely that I would progress to the final two candidates."

Tory grandees are considering changing the rules to limit the number of candidates in the race, which now stands at 12.

A senior member of the 1922 committee of Tory backbenchers told The Independent: “If you can’t get a reasonable number of MPs to sponsor you then you shouldn’t really be the next prime minister.

“If you can’t get 10 friends to nominate you, your closest allies and supporters, then what wider support do you have?"

The MP suggested the threshold for candidates could be 10 supporters.