Keir Starmer today revealed he is quitting as an MP after being ousted from No10 by Andy Burnham.

The former PM previously insisted he would stay on as the member for Holborn and St Pancras.

However, in what could be a final U-turn, he has now opted to resign his seat, triggering a potentially tricky by-election for Labour.

Green Party leader Zack Polanski, a London Assembly member, is considering standing in the contest. His chances appear to have been boosted by a prominent local independent suggesting he is ready to do a deal with 'progressives'. 

New Labour big beast David Miliband has signalled he is not interesting in trying to make a comeback as an MP.  

The move - announced hours before Mr Burnham makes his Commons debut - immediately prompted speculation that Sir Keir could pitch for the Nato general secretary job. 

Allies paid tribute to the former premier's political career. But Mr Burnham sniped at his predecessor by telling Cabinet this morning that the public had noticed a 'change of pace' since he took over. 

Sir Keir told his local paper, the Camden New Journal, that he was ready to 'pass the baton to a successor' and wanted to focus on 'international affairs'.

'It has been a huge honour and privilege to represent the best constituency in the country and to have taken over from Frank Dobson, who was such a great constituency MP and a member of the last Labour government,' he said. 

'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, 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.'

In June Sir Keir's spokesman was adamant that he was 'going to remain' as an MP at least for the rest of the Parliament. 

Sir Keir himself was pressed on the question in an interview and confirmed he would stay on in the Commons. 

The former PM became notorious for his U-turns during his two years in office. He could yet perform another, as despite a previous pledge not to have a resignation honours list allies have refused to rule one out.  

Sir Keir has represented the north London constituency for 11 years, having been director of public prosecutions before entering politics. 

He had a majority of over 11,000 at the general election, but the Greens have been performing strongly in the polls since then. 

A Green Party spokeswoman said: 'Zack (Polanski) has always made it clear he would like to be a London MP. London has been his home for over 20 years.'

Andrew Feinstein, who came second to Sir Keir as an independent candidate in 2024, said: 'We must ensure that all progressive forces in Holborn & St. Pancras unite in order to deliver an MP who represents us & will work for us. An MP who is the antithesis of everything that Starmer stands for.' 

Politics professor Rob Ford said the Greens would 'fancy their chances' and the by-election could be a 'humdinger'.

'Labour's vote dropped 17 points to 48 per cent in this seat in 2024, with a combined 29 per cent going to the Greens (10 per cent) and the left independent Andrew Feinstein (19 per cent). 

'A high profile Green candidate (Polanski?) consolidating that vote would only need a 10 point swing from Lab to win.'

Prof Ford said the local elections this year 'underlined Green strength on the ground in this seat', coming first or a close second in eight of the 11 wards.

'The seat has exceptionally high shares of non-white voters (66 per cent), graduates (51 per cent) and young ppl (47 per cent aged 16-39) - all groups that have swung Lab to Green in recent years. This could be a humdinger of a by-election,' he added.

Comedy candidate Count Binface, who came second to Nigel Farage in last month's Clacton contest, said on social media: 'Can't get a moment's peace on this bloody planet.'

Conservative Party chairman Kevin Hollinrake said: 'Whilst we have disagreed with almost all of Sir Keir Starmer's decisions, I wish him and his family well for the future.

'It is fitting that his final act as a Member of Parliament is yet another U-turn having pledged to stay on.

'The decision to stand down will mean a costly by-election for taxpayers at a time when Andy Burnham and John Healey are plotting tax rises on hardworking families across the country.

'The Conservatives look forward to giving the people of Holborn and St Pancras a chance to vote for a stronger economy and a stronger country in the weeks ahead.'

Meanwhile, Mr Burnham is finally facing a grilling from MPs this afternoon – six weeks after becoming PM.

The premier is making a statement to Parliament as it returns from the summer break.

But he could be in for a torrid time, with anger mounting over the prisoner early release scheme and the prospect of tax hikes to fund more spending.

Ministers have warned of 'difficult' decisions looming in the Budget, as Government borrowing costs spiked again.

Interest rates on 30-year gilts - one of the main ways the Treasury finances debt - hit 5.89 per cent this morning, the highest level since 1998.  

Global markets have been spooked by inflation pressures from the Middle East crisis and fears about an AI crash.

Mr Burnham took over from Keir Starmer just as Parliament went into its break, meaning he has benefited from a 'soft launch' with the public's focus largely on the sunshine instead of politics.

The new leader has gifted Labour a bounce in the polls. However that looks to be fading and the former Greater Manchester mayor has already been forced into a bewildering variety of policy shifts.

According to a Downing Street readout, Mr Burnham kicked off Cabinet by thanking his colleagues for establishing 'a strong sense of momentum' in his first few weeks.

'He said the country have noticed a change of pace with the Government setting the agenda and starting the process of giving local areas the levers they need to create good growth,' the spokesman said.

'He said that during his summer tour, it was clear that life was hard for many people, that they wanted to have hope and hear a positive outlook for the country.'