DAVID Davis has warned Tory MPs that they will lose the next election if they get behind Theresa May’s plans for Brexit.

In a letter to his party’s backbenchers, the former Brexit secretary says “the electoral consequences could be dire” if the Prime Minister’s Chequers plans get through the House of Commons.

Davis’s missive came just hours after May was warned that 40 of her own MPs are prepared to vote down her proposals for Britain’s future relationship with the EU.

If that figure is accurate then it all but scuppers the chances of Parliament accepting any deal she manages to secure from Brussels.

Even one of her cabinet ministers refused to explicitly back the Government’s plans yesterday.

International Development Secretary Penny Mordaunt was repeatedly asked if she supported the Tory leader’s controversial proposals.

Mordaunt, who campaigned for Leave in the 2016 referendum said her boss could count on her support for now: “I think we need to let the Prime Minister and her negotiating team get on with it and I’m supporting her in doing that, I think that’s in the national interest. So I’m not going to give a running commentary on that.”

She added: “All that matters is where we end up, what that agreement is, and I’m going to do everything I can to ensure that is the best deal possible. I feel very strongly that we must honour the result of the referendum and the expectations of the British public in that.”

Former minister Steve Baker, who is the vice-chairman of the Leave backing European Research Group said he knew at least 40 of his Tory MP colleagues who prepared to vote against May’s “half-in, half-out” Brexit.

“Of course the Government are going to whip this vote extremely hard, but what I would say is the whips would be doing incredibly well if they were to halve the numbers, and my estimate is there are at least 40 colleagues who are not going to accept it … or indeed a backstop that leaves us in the internal market or customs union, come what may,” he said.

Baker called the Chequers proposal, which would create a new free-trade area for goods governed by a common EU-UK rulebook, a “half-in, half-out Brexit”.

“I don’t doubt every possible technique is going to be used to sow doubt in colleagues’ minds and to encourage them to vote with the Government. But in the end, the EU is not entitled to split the UK and it’s not entitled to constrain how we manage the economy and govern ourselves after we leave,” he said.

In his letter Davis told MPs that a third way “does exist” that “honours the referendum result, is negotiable with the EU” and which would “reunite” the Tories.

The former minister backs a so-called Canada+++ deal, based on the recent EU-Canada Free Trade Agreement (FTA).

“The Chequers Proposal fails to take back control of our laws, money, borders and trade because it proposes a common rulebook, a facilitated customs arrangement and effective subordination to the European Court of Justice,” Davis wrote.

It would, he said, likely be rejected by Brussels this week forcing the Prime Minister to make further concessions, creating a new “Chequers minus” plan.

The Irish border, he added, was a “red herring” which could be solved by “developing existing administrative procedures”.

“There will be no hard border between the Republic of Ireland and Northern Ireland. It’s that simple,” Davis insisted.

“If we stay on our current trajectory we will go into the next election with the Government having delivered none of the benefits of Brexit, with the country reduced to being a rule-taker from Brussels, and having failed to deliver on a number of promises in the manifesto and in the Lancaster House speech. This will not be a technicality, it will be very obvious to the electorate. The electoral consequences could be dire.”

His successor Dominic Raab said such a plan would lead to the UK crashing out without a deal.

In a statement to the Commons, he told MPs “The EU are not offering us Canada, super Canada, an FTA without keeping to the commitment that we made when he was in Government in December to come up with a legally binding backstop, so that is a shortcut to no deal and we’ve always said that we’d be ready if that outcome is forced on us, but the optimum aim here, the optimum objective that we’re working towards is a good deal with the EU. We couldn’t get that if we pursued what he’s suggesting.”

He also said talks with the EU have “intensified” in recent weeks and the two sides are “closing in on workable solutions”.

Labour said Raab was “pretending” everything is going to plan.