Rishi Sunak has been dealt a fresh blow as one of his aides quit and warned of “at least a decade of Labour rule”.

Will Dry, who was the Prime Minister’s pollster, walked out amid concern over the direction of the Government.

He also claimed the Conservative Party “essentially won’t exist by Christmas” if Nigel Farage returns to frontline politics.

Mr Dry is understood to have quit in November.

In his resignation letter, Mr Dry wrote: “Everyone in this country can see just how colossal the challenges we face are.

“Sadly, it became clear to me we weren’t providing the bold, decisive action required to overcome those challenges. You cannot dent without internalising just how fundamentally broken our political system is.

“I further concluded, again sorrowfully, that the Conservatives are heading for the most almighty of defeats.

“Be in no doubt: we are heading for the most almighty of defeats.

“Be in no doubt: we are on course for at least a decade of Labour rule.

“And if Farage comes back, the Conservative Party essentially won’t exist by Christmas.”

Mr Dry, who was co-founder of Our Future Our Choice, a pro-EU group formed after the Brexit referendum, previously called for a second referendum.

He also demanded Brexit should be halted during negotiations with Brussels.

Speaking at the time, Nigel Farage warned: “Will Dry is one of the most prominent Remain campaigners in the country, so he will feel right at home in Rishi’s No 10. How much more evidence do we need that this Government are selling out on Brexit?”