Former Conservative leader William Hague will back Jeremy Hunt in the Tory leadership race, saying he is “logically and inescapably drawn to vote” for the Foreign Secretary.
Ballot papers will be issued to Conservative Party members from later this week in the contest between Boris Johnson and Mr Hunt.
Mr Hague, who served as leader of the opposition between 1997 and 2001, said he and other members were facing a “decision made more difficult by the knowledge that if we collectively get this wrong there will probably be no further time to correct it”.
He said: “The whole idea of a broad, centre-right party, which has an unbroken history in this country from Robert Peel to Theresa May, is now under threat.
“Serious mistakes in the coming months could be terminal for the world’s most enduring political force.”
The party is facing “immense twin dangers” but many are only focused on one, he said.
“Behind them is the Brexit Party in full cry, threatening electoral calamity if the promised exit hasn’t happened soon.
“But ahead of them is a no-deal Brexit, with its unknown consequences. It is as if a flock of sheep is running full tilt from the wolves while little realising it might be headed for a cliff.”
On the contest, the former Richmond MP wrote in the Daily Telegraph: “Both candidates are committed to a policy that will be formidably hard to implement.
“But one of them has left himself the space in which to do it, even if only a little – an important consideration in a parliament the Tories do not control.
“Whoever wins will benefit from much improved national finances, although I would advise more caution over raiding them in the campaign.”
Mr Hague, now a life peer, said that Mr Johnson’s pledge for Britain to leave the European Union by October 31 on a “do or die” basis had cost him a vote.
“In doing so, however much I wish him well if he is elected, he has lost my vote, because ‘do and then die’ could very easily be the outcome”, he wrote.
“Both men have great merits. But asked to weigh who might make the better prime minister, and have the best chance of avoiding calamity over Brexit, I come to a clear conclusion.
“I will mark my ballot for Jeremy Hunt.”