Zack Polanski, the leader of the Green Party, has announced he wants to contest the Holborn and St Pancras by-election, the parliamentary seat vacated this week by former prime minister Keir Starmer. The move turns what might have been a straightforward Labour hold into a contest that will test whether the Greens can convert recent local momentum into a parliamentary breakthrough in one of London's most progressive constituencies.
Polanski told the Camden New Journal that he hopes to represent the Greens in the central London constituency, a seat Starmer held with an 11,572-vote majority at the 2024 general election. That margin, while comfortable, masked a stronger-than-expected challenge from both the Greens and a left-wing independent candidate, suggesting the seat is not as impregnable for Labour as raw numbers might suggest.
A personal stake in the constituency
Polanski's pitch is rooted in local connection. "I have lived and worked in this community over many years, I know it well and I love it," he said. "It represents so many of the things that make London so special. I am so excited by the prospect of representing this place in Parliament." The emphasis on residency and local knowledge is calculated: it positions him not as a party leader parachuted into a convenient seat, but as someone who can claim genuine roots in the area.
That distinction matters. Holborn and St Pancras covers much of the London Borough of Camden, an area with a long tradition of left-leaning and green politics. The constituency includes parts of Kentish Town, Gospel Oak and Belsize Park alongside the King's Cross development and the British Library quarter. It is the sort of place where Green councillors already exist and where Labour cannot assume that left-leaning voters will automatically fall into line.
Polanski's campaign framing is direct. He said voters will have "someone who will always fight their corner, never scared of big donors or the party whip." The barb at Labour is unmistakable. "Too often Labour has stood up for corporations and big money," he charged. "I will stand up for people struggling to pay their bills." It is a line of attack that Labour under Andy Burnham's leadership will have to answer, particularly in a constituency where cost-of-living pressures remain acute despite its relative affluence.
Starmer's departure and what it leaves behind
Starmer stood down from the House of Commons this week, saying he wanted to devote more attention to international affairs. The statement is diplomatic, but the context is less so. Starmer quit as prime minister earlier this year after losing support within his own party, and his departure from Parliament altogether marks a swift exit from frontline politics for a man who led Labour into government. Andy Burnham, who succeeded him, now faces the awkward business of defending a seat that belonged to his predecessor.
The by-election date has not yet been set. That gives Labour time to select a candidate and organise, but it also gives the Greens and other parties a longer runway to build campaigns. In by-elections, the governing party often suffers a protest vote, and Labour will be conscious that the combination of Starmer's departure, a new leader still establishing authority, and a cost-of-living squeeze creates conditions for an upset, however unlikely that remains on paper.
Starmer's 11,572 majority in 2024 is substantial. But the election saw the Greens and an independent candidate to Starmer's left eat into what would once have been a far larger Labour margin. The constituency's political character, its mix of social housing and expensive private property, its student population and its activist tradition, makes it fertile territory for a Green campaign that can mobilise younger and more disillusioned voters.
Polanski's record and his vulnerabilities
Polanski took over the Green Party last year and has overseen a period of growth. Party membership has increased, and the local elections in May delivered a strong performance, particularly in urban areas where the Greens have traditionally done well. He has been a member of the London Assembly since 2021, scrutinising the mayoralty of Sadiq Khan, which gives him a platform and legislative scrutiny experience that most by-election candidates lack.
But his leadership has not been without difficulty. Polanski has faced scrutiny over the vetting of candidates, a recurring issue for smaller parties that expand quickly and find their selection processes inadequate. He has also attracted attention for his social media posts, the specifics of which have drawn questions about judgment and discipline. In a by-election that will attract national media attention, those vulnerabilities will be examined more closely than they were during local contests.
The local Green Party members must still select Polanski as their candidate. That decision is expected next week. It would be surprising if a sitting party leader were rejected by his own local association, but the requirement is a reminder that Polanski cannot simply anoint himself. A contested selection would generate unhelpful headlines; even an uncontested one invites scrutiny of how the local party reached its decision.
The Green Party's electoral trajectory
The Greens' performance in May's local elections suggested the party has moved beyond its reputation as a vehicle for protest votes in second-order contests. Gains in council seats across England, particularly in university towns and London boroughs, indicated that the party can win when turnout is lower and local issues dominate. A parliamentary by-election is a different proposition: turnout tends to be higher relative to local elections, and the question of who forms the government is absent, which can help smaller parties.
Holborn and St Pancras is not a seat the Greens would have targeted before Starmer's resignation. It was solidly Labour, held by the party leader, and would have been defended vigorously in any normal circumstance. But the circumstances are not normal. Starmer's departure removes the incumbency advantage of a former prime minister. The new Labour candidate will lack his profile. And the by-election will be fought in a political environment where Labour, now led by Burnham, must defend a record in government that includes the economic difficulties Starmer struggled to resolve.
For the Greens, the calculation is straightforward. Even a strong second place would be a signal that the party can compete in parliamentary contests beyond its existing handful of seats. A win, while still unlikely given the size of the majority, would be a political earthquake. The party's best realistic outcome may be to narrow the margin sufficiently to demonstrate that Labour's hold on progressive urban seats is conditional.
Labour's dilemma in its own backyard
Labour faces an awkward set of choices. Burnham's government must defend a seat that belonged to the man he replaced, in a constituency where left-leaning voters have already shown willingness to look elsewhere. The temptation will be to dismiss Polanski as a party leader seeking a parliamentary shortcut, but that line of attack risks sounding dismissive of the genuine Green support that exists in the area.
The more substantive challenge for Labour is policy-based. Polanski's accusation that Labour stands up for "corporations and big money" rather than people struggling with bills is the kind of charge that resonates in a constituency where food bank use has risen alongside property prices. Labour's response will need to be more than procedural: pointing out that the Greens are unlikely to win the seat will not satisfy voters who are drawn to Green policies on housing, energy and local services.
There is also the question of the independent left. In 2024, a left-wing independent candidate took a significant share of the vote in Holborn and St Pancras. If that tendency fields a candidate again, the anti-Labour vote will be split, which would help Labour. If it does not, and those voters consolidate behind the Greens, the arithmetic becomes more interesting. The Office for National Statistics has documented the cost-of-living pressures that provide the backdrop to this contest, and any candidate who can speak credibly to those pressures will find an audience.
What the numbers really show
An 11,572 majority looks commanding, and in most circumstances it would be. But context matters. Starmer was party leader and prime minister, advantages that boosted his personal vote beyond what a standard Labour candidate could expect. The 2024 result also came during a general election when the question of who would form the government concentrated minds. A by-election removes both of those factors.
The Greens' performance in May's local elections provides a benchmark. In Camden, Green councillors already represent wards within the constituency. That local infrastructure matters: it means the party has organisers, canvassers and name recognition on the ground, not just a national profile. Polanski's own visibility as party leader adds to that, though it also makes him a target for scrutiny that a local candidate would escape.
The broader question is whether the Greens can translate local election success into parliamentary contests. Historically, the party has struggled with this transition. Its four MPs were elected in seats where years of local campaigning built a foundation that general election turnout could not wash away. Holborn and St Pancras does not yet have that foundation, but it is closer than most constituencies.
The campaign ahead
Much depends on timing. The by-election date has not been announced, and Labour will want to move quickly to deny opponents the chance to build momentum. Polanski's selection, expected next week, will determine whether the Greens enter the contest with a unified campaign or with internal questions about their candidate. The independent left's decision on whether to field a candidate could prove decisive: a split anti-Labour vote helps the governing party; a consolidated one makes the contest competitive.
For Labour, the priority is to avoid the appearance of complacency. A governing party that takes a safe seat for granted in a by-election often pays for it. Burnham's team will need to select a strong local candidate quickly and run a campaign that addresses the cost-of-living concerns Polanski is already targeting, rather than assuming the majority will hold itself.
People mentioned
Organisations
Green Party · Labour Party · London Assembly
