Sir Keir Starmer has announced he is to stand down as MP for Holborn and St Pancras, a move that will trigger a by-election in the London seat.

In a statement to the Camden New Journal newspaper, he said it had been a “huge honour and privilege” to represent the constituency for 11 years but he would now turn his focus to “international affairs”.

Sir Keir stood down as prime minister earlier in the summer, with Andy Burnham replacing him.

It follows weeks of speculation about whether Sir Keir would remain as MP following his resignation.

In a BBC interview shortly after stepping down as PM, Sir Keir said he would stay as an MP until the next general election, which must take place by 2029.

But in his statement, external released on Tuesday, Sir Keir said he was ready to “pass the baton to a successor”.

He added: “I will now focus on other things and that will be international affairs including defence, security, trade and technology in a fast-changing world.

“I will also continue, as I have done for a long time now with others, to work on combating violence against women and girls; that is an issue that matters to me hugely.

“It’s work I started before I became an MP and it’s work I’m keen to continue after I’m an MP. So international affairs on the one hand, and continuing my work on violence against women and girls on the other.”

Sir Keir’s announcement comes hours before Burnham is due to deliver his first statement in the Commons as prime minister, setting out his priorities and taking questions from MPs.

A date will not be set for the by-election until Sir Keir formally resigns his Commons seat.

Holborn and St Pancras has long been a Labour stronghold, with Sir Keir securing a more than 11,000-vote majority in the 2024 general election.

Conservative chairman Kevin Hollinrake accused Sir Keir of making “another U-turn having pledged to stay on”, prompting a “costly by-election for taxpayers”.

While it is unclear exactly what type of international affairs role Sir Keir may take up, global issues and diplomacy dominated his time as PM.

In his departure interview in July, Sir Keir was asked if he had another big political or international job in him, to which he replied: “I don’t know is the honest answer to that.”

By standing down so soon after quitting as PM, Sir Keir has departed from recent precedent for those in Downing Street before him.

Rishi Sunak is still the Tory MP for Richmond and Northallerton two years after leaving No 10, and his precedessor Liz Truss stayed on as a backbencher until she lost her seat to Labour at the 2024 election.

Theresa May stayed on as MP for five years after leaving Downing Street.

However, both Boris Johnson and David Cameron quit the Commons shortly afterwards.