Temerko, who has praised Johnson in the past, said the government’s domestic policies were “absolutely populist”, that “any party would do the same” in the run-up to an election, and that they amounted to “nothing new, nothing exciting”.

Speaking to HuffPost UK, the Ukrainian-born donor said: “There is only one slogan that the party today is fanatically promoting: that is leave Europe with or without a deal.

“October 31 is Boris Johnson’s day of death.

“Today the party is mostly not a centre ground party at all, it is turning more and more into a politically religious sect with just one idea – the idea of Brexit as the only one god.

“We are Christian or Muslim or Jewish – we have another god, Brexit is not our god.

“That is a big problem and the people who can keep the party in the centre ground are on the outside.”

He added: “It’s absolutely crucial if we want to be an attractive national party with a successful political future.”

Like many in the party, he criticised Johnson for suspending parliament until October 14 and suggested Cummings, the PM’s chief of staff, was behind the PM’s more extreme actions, including the purge of rebels.

“He is like the archbishop of this sect,” Temerko said of Cummings.