VINCE Cable will today claim that Brexiteers like Boris Johnson and Jacob Rees-Mogg will seek to justify years of Brexit-induced economic pain because they have experienced the “erotic spasm” of Britain leaving the EU.

In a keynote speech at his party’s conference, the Liberal Democrat leader will claim European leaders now pity Theresa May because they know the Prime Minister is delivering a policy she does not believe in and that she knows deep down Brexit is a bad idea.

In an appearance at the annual Lib Dem gathering in Brighton that could turn out to be Sir Vince’s last as leader, the 75-year-old grandee will aim his sights firmly on the Tory Brexiteers and his party’s campaign to give people a chance to “exit Brexit”.

He will say: “For the ‘true believers’ – the fundamentalists – the costs of Brexit have always been irrelevant: years of economic pain justified by the erotic spasm of leaving the European Union. Economic pain felt, of course, not by them but by those least able to afford it.”

Sir Vince will note that voters do not mind what the Brexiteers dream about behind closed doors, “so long as their dreams don’t become nightmares for the rest of us”.

He will declare: “It really beggars belief that the Army and police are now being asked to prepare for riots in the chaotic aftermath of a botched Brexit. And billions – billions – of taxpayers’ money spent preparing for disaster.”

The party leader will also denounce the “latest piece of nastiness from Jacob Rees-Mogg, calling into question the right of Europeans to stay in Britain and of Britons to stay in Europe; creating unnecessary worry and insecurity for millions”.

Sir Vince will tell his party’s delegates in Brighton that people know when the Government has gone seriously wrong when they start feeling sympathy for the PM because of the pressure she is put under from the warring factions of the Conservative Party; proof, he will assert, that the Tory Government is broken.

“I would go so far as to say that some of us are starting to feel sorry for the Prime Minister. It seems that even the European leaders are moved to pity; it is obvious why.

“She is dutifully delivering a policy she doesn’t really believe in; failing in negotiations, losing public support and all to appease a dwindling group of angry people in her party who will denounce her as a traitor, whatever she comes up with.”

He will go on: “But when we feel sorry for the country’s Prime Minister, something is seriously wrong. Our sympathy can only extend so far, while she puts the interests of the country second to the whims of the extremists in her party.”

The Lib Dem leader will claim that “deep down” Mrs May knows Brexit is a bad idea.

“A bad idea whose time has gone,” he will declare. “Even now, Theresa May could shock us all, by displaying true leadership. She could admit that the Brexit project has gone badly wrong.”

Sir Vince will argue that any deal or no deal that the PM brings back from Brussels is not going to be better for Britain than remaining in the European Union.

“Instead of kowtowing to her enemies in the Conservative Party, she could lead her party and the country by opening her mind to a ‘People’s Vote’ on the final deal,” he will add.