The Prime Minister is facing a new crisis after his party was pushed into third place behind the Green Party and Reform UK. Mr Turner told BBC Radio 4's Today programme: "Well it's catastrophic, isn't it? I mean, that's the truth. It couldn't be any worse.

"Having the Greens in Manchester is the worst result we could have expected or we wanted, frankly. But you know, the reality is, Burnham was blocked. He shouldn't have been, in my view."

Mr Turner blamed "unpopular" policies and the Gaza row for Labour coming third in the former stronghold.

He said: "This is the stuff on Gaza and Palestine and a build-up of policy which is unpopular.

"And frankly the fact that Andy Burnham was blocked, who was the candidate who gave us our best chance, that's why we are where we."

Richard Burgon, who is secretary of the Socialist Campaign Group of Labour MPs, said the blame "lies squarely with Keir Starmer and his clique".

The left-wing Labour MP added: "They put factional interests over having the candidate best placed to win, Andy Burnham.

"If Labour is to be the “Stop Reform” party, then the leadership must stop treating progressive voters with contempt - and start appealing to them.

"That means a return to real Labour values - through policies like a Wealth Tax, public ownership of energy and water, and an ethical foreign policy that are all popular with the public.

"And it means ditching the approach of trying to ape Reform and kicking the left, that has alienated so many people who have voted Labour previously."

Labour Party chairwoman Anna Turley described the result as "clearly disappointing".

She said: "By-elections are normally difficult for the party of government, and this election was no different."