President Donald Trump said that outgoing UK Prime Minister Keir Starmer 'failed badly' in his two year tenure as leader, with the left-leaning politician now throwing America's greatest ally into political turmoil. 

Starmer announced his resignation on Monday as he faced a mutiny inside his own party following the by-election win of former Greater Manchester Mayor Andy Burnham, who is now clear favorite to succeed him. 

Trump waded in on the crisis that engulfed Downing Street on Sunday in a post to Truth Social in which he attacked Starmer's record in office. 

'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', he said.

The pair met just last week at a gathering of G7 leaders at a summit in France after they had a falling out when Starmer refused to let the US use British military bases to carry out strikes on Iran, and his decision not to send aircraft carriers to the Middle East. 

Relations were further strained when Vice President JD Vance intervened in UK politics, with Starmer's office criticizing those seeking to 'interfere in our democracy'. 

Starmer held back tears as he announced he was standing down from his post, as he talked up his achievements in getting the Labour Party elected to power. 

But he acknowledged that his time had run out. 'I know the question being asked now is not who is best placed to change the Labour Party... the question my party is asking now is whether I am best placed to lead us into the next general election.'

He added: 'I accept that answer with good grace... that is why I will resign as leader of the Labour Party.' 

Starmer said there would be an 'orderly' process to choose his replacement. He said a successor would be in place before the House of Commons summer recess on July 16 if there is only one candidate - Burnham. Otherwise the decision could take until August.

Starmer became emotional as he paid tribute to the support from his family - saying he would now focus on being the 'best husband' and the 'best dad'. 

Wife Victoria and the couple's son had joined close colleagues outside in the street to watch the news being delivered. 

Burnham - who has rallied huge support from Labour MPs since romping home in the Makerfield by-election last week - is due to be sworn in at the Commons today. The pair are not thought to have spoken directly for months. 

Nigel Farage, leader of the Reform Party and a friend of Trump, called for a general election to accompany the change at the top. 

The PM returned to Downing Street from Chequers, the country home of the Prime Minister, on Monday morning, after spending the weekend locked in talks with wife Victoria and close aides. 

He spoke to King Charles III, who is at his Highgrove residence, by phone before making the announcement.

Sir Keir reiterated his defiance on Friday after Burnham stunned the political world by securing a 9,000 majority over Reform in Makerfield.

He insisted he would fight any challenge to his leadership. 

But the mood music had dramatically shifted by yesterday, when Business Secretary Peter Kyle - a Starmer loyalist - was sent on TV to say the premier was reflecting on his situation. 

In his speech this morning, Sir Keir said: 'Walking up this street two years ago was the proudest moment of my life, a new Labour government, the first in 14 years, a page in our country's history turned after years of disappointment and despair, the chance to change the lives of millions of people for the better, that's what I came into politics for the journey to that point was not easy.

'Six years ago, I inherited a Labour Party that was politically, financially, and thoroughly bankrupt.

'I was told time and time again that my party was finished, that we were consigned to history, that a majority at the general election, let alone a landslide majority, was impossible, but we proved those people wrong, because we changed our party, ripping out the poison of antisemitism, restoring trust on the economy, defense, and national security, and becoming a party that once again stood proudly with, not against, our national flag.'

Sir Keir insisted that people should 'look at what we've achieved in just two years'.

'An economy that is stronger, going faster than our peers, wages rising faster than inflation in every single month since we came to power,' he said.

'Investment secured, infrastructure being built, an end to austerity with the fastest fall in NHS waiting lists for 17 years, the biggest improvement in rights for workers and renters in a generation.'

'The biggest uplift in defense spending since the Cold War.

'Small boat crossings falling, asylum hotels closing, protecting young people from social media and half a million children being lifted out of poverty because of the choices that I made.

'Our reputation in the world restored, with Britain once again standing up for decency, respect and the rule of law, securing trade deals, standing with Ukraine, standing up for our values and rebuilding our relationship with our allies in Europe.

'Change promised by a Labour government. Change fought for by a Labour government. Change delivered by a Labour government.'

His voice cracking, Sir Keir said: 'I want to thank the brilliant Number 10 staff and our country's extraordinary Civil Service who dedicate their lives to public service.

'And when I leave the biggest job in the country, I shall spend more time on the most important job, being the best husband I can to my fantastic wife, Vic, who has been a rock by my side through good times and bad, and being the best dad I can to my beautiful children, who are my pride and my joy.'

Burnham has committed to slashing business rates for pubs and hospitality venues, nationalizing water, energy and transport, a massive investment in council housing and a revival of the northern leg of HS2, a high speed rail project.

Burnham is yet to outline how he will pay for these promises, made in the heat of his by-election campaign, which could cost taxpayers tens of billions of pounds.