BORIS Johnson has been warned by Tory former attorney general Dominic Grieve that Conservative MPs could push him out of office in October if he becomes prime minister and tries to exit the UK from the EU with no deal.

In a thinly veiled threat to the front runner in the race for Number 10, Grieve insisted a large number of Tory MPs would mobilise to prevent a no-deal Brexit in the autumn.

He told BBC Radio 4's Today programme: "If the new prime minister announces taking the country on a magical mystery tour towards an October 31 crash-out, I don't think that prime minister is going to survive very long.

"Of course, the prime minister could exercise his absolute right of then going to the country and having a general election.

"But that is likely to be catastrophic for the future of the Conservative Party."

Asked if he could vote against the Government in a no-confidence motion in order to try and prevent a no-deal exit from the EU, Grieve said: "If a prime minister insists that they are going to crash us out of the European Union on October 31 with no deal... then I am pretty sure that 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."

Pressed on whether the Queen would then need to get involved, Mr Grieve said: "It is worth bearing in mind that if an administration falls on a vote of no confidence, there is 14 days to set up a new one."

He added: "No, 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.

"There has to be a confidence vote in those circumstances.

"If that were to happen under the Fixed Term Parliaments Act, the person who is prime minister, their tenure in office comes to an end and a new administration can be formed in that period.

"And it might concentrate minds wonderfully on the need to have an administration run by somebody who has a tenable policy."