Sir Keir Starmer will resign after “failing badly” on migration, Donald Trump has said. The US president attacked the Prime Minister amid speculation that he would announce his departure from No 10 as soon as tomorrow.

Writing on his Truth Social platform, Mr Trump said: “Keir Starmer will resign as Prime Minister of the United Kingdom.

“He failed badly on two very important subjects – IMMIGRATION AND ENERGY (OPEN NORTH SEA OIL!). I wish him well! President DJT.”

Mr Trump and Sir Keir have clashed repeatedly over the two topics in the past 18 months, with the US president calling on the Prime Minister to adopt a stricter border policy.

Last month, Mr Trump said it would be “tough” for Sir Keir to survive Labour’s historic defeat in the local election, and called on him to “straighten out immigration” and restart drilling in the North Sea if he wanted to survive.

Meanwhile, Andy Burnham has been mocked as a flip-flopper who would take Britain in the “wrong direction”.

The warning comes amid expectations that he will replace Sir Keir Starmer, who could quit as Prime Minister as soon as tomorrow.

Mr Burnham will make a dramatic return to Westminster on Monday to be sworn in as an MP following his victory in last week’s Makerfield by-election.

He is also planning to deliver a rallying-cry to Labour backbenchers.

His return is likely to trigger Sir Keir’s departure following a catastrophic time as Prime Minister.

But critics have warned that the British public don’t know what he stands for.

Shadow Chancellor Sir Mel Stride, told the BBC: “My concern about Andy Burnham is the flip flopping.

“My concern about Andy Burnham is that he does not seem to know what the fiscal rules are.

“You have seen some of the market reaction, the bond market reaction, to Andy Burnham which is to increase our borrowing costs – that is higher costs for people with their mortgages and businesses, borrowing costs, and so on – plus a lot of what appeared to be unfunded commitments, that he puts out there and then resiles from later when somebody tells them that it all just does not add up.

“None of that, I’m afraid, fills me with any confidence.”

He added: “I think the concern that I have is, in terms of what is good for the country, even if we have a change of Prime Minister now, and that looks increasingly likely – what is going to follow?”

Around 100 Labour MPs have publicly called on Sir Keir to set out a timetable for his departure.

Cabinet Ministers have also privately pressured the PM to make way for Mr Burnham who is rallying mass support.

It is not yet clear that, if the Labour leader resigns, he will go immediately or have a longer “orderly” exit during the summer.

It is understood Mr Burnham’s camp wants Sir Keir to set out his plans in the coming days but would accept a timetable that kept him in No 10 until September.

Sources insisted on Sunday that Sir Keir, who spent the weekend discussing his future with his wife Victoria at the PM’s country retreat Chequers, had yet to make a final decision about his future.

But one of his Cabinet allies failed to deny claims that he is poised to quit amid feverish speculation about his future.

Peter Kyle, the Business Secretary, said the Prime Minister is reflecting on the “political realities” he now faces.

This is a stark change from 48 hours earlier when Sir Keir vowed not to walk away from his post in the immediate aftermath of Mr Burnham’s by-election victory.

Pressure has been mounting for weeks Cabinet minister’s Wes Streeting, the former Health Secretary, and ex-Defence Secretary, John Healey, plus a number of junior ministers, resigning since Labour’s humiliating local elections defeats in May.

Labour grandees have also spoken out, with former home secretary Alan Johnson saying Sir Keir should step aside and Lord Falconer saying he has “no authority” because it is assumed he will be replaced by Mr Burnham.

Mr Kyle told broadcasters on Sunday he had not spoken to the Prime Minister since Friday, when he had a “frank conversation” with him.

Asked about reports Sir Keir is planning to announce his resignation as soon as the coming week, he told the Sunday with Laura Kuenssberg programme that “whatever unfolds” in the coming days will be a “functional process”.

“I don’t know what’s going to unfold in the days that lie ahead. I don’t know the decisions that he will make on behalf of our country as he considers these issues, and then makes decisions.

“But we will find a way for this to be whatever unfolds, a functional process, one where the Labour Party is seen to put the interests of the country first and foremost, and we will carry on delivering for this country through whatever does unfold in the days ahead.”

But asked if the Prime Minister still plans to fight a leadership challenge, Mr Kyle said “these are decisions for Keir to make” and repeated the PM is “taking the time to think through what the political realities are today compared to last week, the week before”.

Sir Keir warned Labour staffers during a call on Friday lunchtime to avoid “plunging our party and our country into chaos by turning on each other and tearing apart our party and our movement”.

Foreign Secretary Yvette Cooper is among Cabinet ministers reported to have told him he should set out a timetable for his departure.

She declined to comment.

Transport Secretary, Heidi Alexander, Home Secretary, Shabana Mahmood and Energy Secretary, Ed Miliband are all understood to have told the Prime Minister that his time is up.

If Sir Keir does not resign, 81 MPs would need to line up behind a candidate to trigger a leadership contest and former health secretary Wes Streeting suggested last week he would be willing to fire the starting gun on such a process.

Labour MP Toby Perkins, a Starmer loyalist, said it needs to be clear whether a new leader would take the party on a “radical departure” from the manifesto it was elected on.

Former minister Jess Phillips, meanwhile, said candidates should at least present their ideas to the Parliamentary Labour Party.

“I very much hope that over the next week, at least, that whilst we may not end up with a full-scale contest, that there is an opportunity to properly question, in somewhat of a public forum, what’s coming next?,” she told the BBC.