Tories will bring Boris Johnson down if he pursues no-deal Brexit, warns Dominic Grieve

‘If the new prime minister announces a magical mystery tour towards a 31 October crash out, I don’t think that prime minister is going to survive very long’

A senior Conservative MP has warned Boris Johnson he will not “survive very long” if he pursues a “crash-out” Brexit, because fellow Tories will bring him down.

Dominic Grieve, who supports Britain remaining in the EU, predicted “a large number” of his colleagues would turn on the new prime minister, even joining a vote of no confidence to block a no-deal exit.

“There are a large number of Conservative MPs who will object to that happening and who will do everything possible to prevent it happening. I think the numbers are quite substantial,” the former attorney general said.

Mr Grieve admitted the new prime minister – widely expected to be Mr Johnson – could call a general election to win the public’s backing a for a no deal, if thwarted in parliament.

But he warned the Tories would lose badly, saying: “That is likely to be catastrophic for the future of the Conservative Party.”

Mr Johnson entered the Tory leadership race vowing to deliver Brexit by 31 October “deal or no deal”, but has since appeared to waver on that commitment.

Underlining the confusion, some Tory MPs have emerged from meetings with the leadership favourite convinced he would willingly crash out of the EU – while others were reassured he would pursue an orderly departure.

Mr Grieve told BBC Radio 4: “If the new prime minister announces taking the country on a magical mystery tour towards a 31 October crash out, I don't think that prime minister is going to survive very long.”

However, he pointed out that a successful no-confidence motion – which Labour has threatened to bring within days of Theresa May’s replacement being in place – would not necessarily put Jeremy Corbyn in No 10.

“If an administration falls on a vote of no confidence, there is 14 days to set up a new one,” Mr Grieve explained, adding: “It doesn't have to be Jeremy Corbyn at the helm.

“It could be another Conservative prime minister. It could be anybody who is able to command a majority in the House of Commons.”

Mr Grieve said the threat of a no-confidence defeat “might concentrate minds wonderfully on the need to have an administration run by somebody who has a tenable policy”.

Both Philip Hammond, the chancellor, and Ken Clarke, a former chancellor, have suggested they would join a no-confidence vote to thwart crashing out of the EU.

Furthermore, 26 Tories backed outsider Rory Stewart, who is committed to avoiding a no deal – while two were so disgusted with the choice of surviving candidates, after Mr Stewart was knocked out, that they spoiled their ballot papers.

Some Labour figures believe Mr Corbyn will step back from a no-confidence vote next month, believing the chances of success are greater in the autumn, as the Halloween deadline looms.

The new prime minister is expected to be unveiled on 23 July – two days before MPs leave for their five-week summer recess.