“The present situation only ends one of two ways,” the normally-loyal Labour MP told HuffPost UK. “Either Rachel goes or Keir goes.”

As Keir Starmer approaches his first anniversary as prime minister, the question of how much longer he can last is now being openly debated at Westminster.

It is a remarkable turnaround, just 12 months after he led Labour to a landslide election victory which left him with a barely-believable 165-seat Commons majority.

The events of the last month have led many of those MPs who were elected last July to reluctantly come to the conclusion that Starmer is not the man to lead them into the next election.

“He should have three years to turn it around, but if he keeps going like this he won’t get those three years,” said one source.

The PM has U-turned on no fewer than three occasions in the past month alone – on winter fuel payments, whether to hold a national inquiry into child grooming gangs and, in the last 24 hours, over cuts to the welfare budget.

Labour MPs fear Starmer is now a prime minister who is buffeted by events rather than one who makes the political weather, and are demanding big changes to the way he goes about his business.

“We were told to support taking winter fuel payments off millions of pensioners, and to vote against a national grooming gangs inquiry, and then at the first sign of trouble he folds,” said one exasperated MP. “That makes a lot of us very angry.”

Labour MPs bemoan the fact that Starmer is never seen around parliament, meaning opportunities for impromptu chats with him are few and far between. As if to confirm this, it emerged this week that the PM has only voted in the Commons seven times since entering No.10.

The ever-ambitious Wes Streeting, others point out, is a familiar face around parliament.

Neil Duncan-Jordan told Radio 5Live this week that since being elected the MP for Poole last year, he has not spoken to Starmer once.

A Labour veteran told HuffPost UK: “That is unbelievable. After 1997, Tony Blair had every new MP in to No.10 for a cup of tea and to say thank you. It cost nothing and built up a lot of goodwill that came in handy down the line.”

Another Labour insider described the No.10 operation as “completely dysfunctional”.

“It’s a mixture of ignorance and arrogance,” he said. “They think all they need to do is send out instructions and all those MPs they put into seats will do as they’re told, but it doesn’t work like that.”

It isn’t hard to find Labour MPs who are especially critical of Morgan McSweeney, a man virtually unknown outside the Westminster bubble but who, as Starmer’s chief of staff and top adviser, wields enormous power in No.10.

The finger of blame has been pointed at him over the welfare debacle, when Starmer was forced to water down plans to cut £5 billion from the benefits budget in the face of a rebellion by more than 120 Labour backbenchers.

McSweeney’s critics accuse him of being an authoritarian, someone who lays down the law and expects others to follow it rather than attempting to bring people along with him through persuasion and discussion.

One MP said: “At the end of the day, Keir needs to say to Morgan McSweeney ‘it’s either you or me, and it ain’t going to be me’.”

An ally of McSweeney defended him, however, pointing out that a number of those involved in the rebellion have never reconciled themselves to Starmer’s leadership and simply want “regime change” in No.10.

Others in government believe the blame for the welfare U-turn should be laid at the door of the Treasury, which demanded the cuts to help chancellor Rachel Reeves fill her £22 billion black hole.

In particular, they believe the chancellor was wrong to take another £500,000 out of the welfare budget to make her sums add up on the eve of the Spring Statement in March.

“That was a huge mistake,” said one senior government source. “There’s a lot of good stuff in the welfare reforms about getting people off a life of benefits and into work, but that was completely lost in all the talk about cuts.”

The irony is that Starmer’s climbdown on the welfare reforms could cost as much as £3 billion, money which Reeves will have to find from somewhere ahead of the Budget in October, most likely through more tax rises.

That is another reason why many in Labour believe the PM’s close political alliance with his chancellor could finally be coming to an end.

“Rachel is done,” said one source. “The question now is whether he shoots her to try and save himself, or whether he doesn’t do it quickly enough as usual.”

The bad news for Starmer is that he may not even be close to hitting rock bottom yet.

Plans to cut the amount of money the state currently spends on supporting children with special educational needs will be brought forward before the end of the year.

Those familiar with the details say they will prove to be even more controversial than the welfare cuts, teeing up yet another clash with Labour MPs who now believe the PM will fold if they apply enough pressure.

The real crunch is likely to come next May, however, when elections will take place across the UK.

Were Labour, as seems likely at the moment, to lose power in the Welsh Senedd, fail to defeat the SNP in Scotland and lose control of more councils in England, then the knives really will be out for Starmer.

“The next few weeks will be choppy, but next May is the real ball game,” said one Labour source.

With Streeting and Angela Rayner among those waiting in the wings, could Starmer face a leadership challenge?

An ally of the prime minister insisted there was no concern about his position inside 10 Downing Street.

“The strategy of taking difficult decisions now in order to reap the benefits further down the line remains in place,” he said.

“What difference is a new leader going to make? Will they just take the bond markets out for a pint and say ‘go easy on us, we’ve got a new prime minister’? That is fundamentally unserious.”

Starmer’s immediate future may be secure, but the number of Labour MPs now speculating about how long he has left should worry No.10.

His first year in office has been marked by a series of mistakes, rows and U-turns, and there is little sign of things improving in the months ahead.

The PM needs his luck to change, and soon.