US President Donald Trump has said that UK Prime Minister Keir Starmer will resign from his office, citing failures on immigration and energy policies, amid widespread speculation that the UK leader could set out a timeline for his departure as soon as Monday.

"Keir Starmer will resign as Prime Minister of The United Kingdom," Trump wrote on his Truth Social platform.

"He failed badly on two very important subjects- IMMIGRATION AND ENERGY (OPEN NORTH SEA OIL!). I wish him well!"

Earlier on Sunday, the BBC reported that Starmer could set out a timetable to step down as early as Monday, as the mood within the government shifts.

Several government insiders now believe the British prime minister could announce a timetable for resignation as soon as Monday, according to the report.

White House scolding over domestic policy

In his social media post, Trump criticised Starmer, the leader of the UK’s centre-left Labour Party, saying ineffective policymaking would be behind his political demise.

Trump has repeatedly urged the British government to reverse its freeze on issuing new oil and gas exploration licences in the North Sea, and he has criticised the UK's wind farms.

Though he was once nicknamed the "Trump whisperer" on account of his apparent ability to keep the president on-side, Starmer has recently been subject to a deluge of scolding from his American counterpart regarding the war in Iran.