Burnham’s Labour faces first big test as Polanski eyes Starmer’s old seat

The resignation of Keir Starmer as an MP has triggered a byelection that looks set to become the first real test of the “Burnham bounce” – and a serious opportunity for the Green Party to make its long-awaited breakthrough in London.

Starmer announced on Tuesday that it was “the right time” to step down after 11 years representing Holborn and St Pancras, telling the Camden New Journal that it had been an honour to take over from Frank Dobson, the seat’s only other MP since it was created in 1983. He was formally appointed steward of the Chiltern Hundreds the same day, the procedural device used to vacate a Commons seat.

Green Party leader Zack Polanski moved fast, confirming his candidacy within 48 hours. He has said the contest will be “a referendum on ending Rip-off Britain” and told the same Camden New Journal that he was “excited by the prospect of representing this place in parliament”. Polanski, currently a London Assembly member, will almost certainly be unopposed for the Green nomination, with the party expected to formally confirm him within the week.

A look at the numbers explains his interest. Starmer’s 2024 majority of more than 11,000 masked a collapse in Labour’s vote share, down 17 points on 2019 to 48.9%. The Greens finished third with 10.4%, behind independent Andrew Feinstein. In May’s Camden local elections, that gap narrowed sharply. Labour took 38.8% across the seat’s wards to the Greens’ 28.8%. Feinstein, who this week ruled out standing again, said in July that whoever replaced Starmer should be “the antithesis of Starmer in every possible way” – a sentiment Polanski’s campaign will be keen to inherit.

Labour’s selection contest will be very closely watched

For Labour, the byelection lands awkwardly. The party is yet to select a candidate, with a decision expected on 9 September. David Miliband has reportedly turned down the chance to stand and speculation has settled on Camden council leader Sagal Abdi-Wali, a Starmer ally and former chair of his constituency party. How Labour’s selection is handled will matter as much as who wins it. A contest widely seen as parachuting in a favoured continuity candidate would hand Polanski’s team an easy line of attack, particularly among members and voters who backed Andy Burnham’s leadership bid partly on a promise of change from the Starmer years.

That points to the real subplot of this byelection: whether Burnham’s early polling recovery – with Labour moving from behind Reform UK to level or ahead in several recent polls – can survive contact with a real ballot box. A comfortable Labour hold would let Burnham claim the bounce is real. A shock result, or even a narrow win, would hand fresh ammunition to Starmer’s old warning that Burnham risks another Truss-style shock to the economy and the party’s standing.

For the Greens, the strategic logic is straightforward. Position Polanski not as an alternative to Labour in opposition, but as pressure on a Labour government from its left flank. Something close to “keep Burnham honest” messaging would fit both the seat’s demographics – a young, graduate-heavy, pro-Palestinian electorate – and Polanski’s own positioning of the Greens nationally as an eco-populist left alternative rather than a party of protest alone.

No date has yet been set for the byelection, and no polling has been published. But with Labour’s candidate unconfirmed, Feinstein out of the running and Polanski already campaigning, this is shaping up as one of the most closely watched contests of the parliament so far.