Nick Clegg has conceded defeat in his fight to keep Britain in the EU’s Single Market and Customs Union and admitted that ‘soft Brexit’ is dead.

The former deputy prime minister attacked Brexiteers as “very rich, very angry old men” before comparing them to Bolsheviks who had no mandate for hard Brexit.

Theresa May would be victorious in creating a Britain free of the influence of Brussels, Sir Nick told the Lisbon Council think tank on Monday evening, but he called on Westminster MPs to vote down her final Brexit deal.

“This week is the week that the illusion of a so-called soft Brexit has died,” he said after Mrs May reiterated that Britain would not seek continued membership of the customs union.

Sir Nick, a former MEP and committed Europhile, said: “It was always a nonsense in my view, but there was a feeling that maybe Theresa May would pluck up courage that she’s never displayed hitherto to defy her right-wing.

“There was a slight sense that she was starting to realise the error of her preemptive declaration of red lines, [that this] was going to lead her to try and sue for peace on an emollient basis.”

Mrs May has always insisted that Britain would leave both the Single Market and Customs Union because that would be the only way the UK could regain control of its immigration and trade policy.