But the real reason for the nocturnal scramble of cameras, microphones and questions for Polanski had little to do with the by-election – and everything to do with a vote at the Green Party’s conference in Brighton last weekend.
Activists there passed a motion declaring Zionism as a form of racism.
The motion defined Zionism as an ideology supporting “an ethnonationalist Jewish state” and backed a “single democratic Palestinian state in all of historic Palestine”, which includes modern-day Israel.
Polanski didn’t take part in the vote because, he said, he chose to campaign in Holborn and St Pancras instead. And he repeatedly declined to do interviews, as the pressure on him as ratcheted up.
But this morning he did speak to journalists.
He told Breakfast that if he had he been there for the vote he “would have voted for the amendments”.
Asked if he would have voted against the motion in the hall on that day, Polanski said: “the motion as amended I would have voted for, the motion unamended I wouldn’t have voted for.”
He added: “I think it’s an imperfect motion, there’s parts I disagree with and parts I agree with.”
Some in the party are furious about what has happened in recent days, with one figure telling me: “He has created a monster he either can’t or won’t control.”
Green Party membership has increased more than three fold in the last year and internal critics of Polanski say this includes hard-left campaigners focused on the Middle East rather than environmental concerns.
Within the party and beyond it, a row is now boiling. Polanski, who is himself Jewish, has been banned from Israel. The Jewish Leadership Council and the Board of Deputies of British Jews have criticised the party, as have sister Green parties in Europe.
And – significantly – the former party leader and one of the most important figures in the Green movement of her generation, Caroline Lucas, told Newsnight Polanski had failed to show leadership over the issue. She also failed to back him carrying on as leader.
Asked by reporters after the by-election result if he could continue as leader, Polanski insisted “of course I can carry on”.
He did not explicitly reject the motion his party has passed, saying there was an “ongoing genocide and the displacement of the Palestinian people”.
“I believe that is clearly racist,” he added.
Israel has repeatedly denied its actions in Gaza amount to genocide.
And asked if he believed in a two-state solution – an Israeli and Palestinian state existing peacefully alongside each other – he said “I believe it is not our role to decide”.
He repeated that “it is my job to reassure people and make sure that we bring our party together”.
“No one will be excluded in the Green Party based on faith and religion,” he said.
But Polanski now confronts the greatest crisis of his leadership so far. He faces open, public insurrection about his judgement from senior figures internally and opprobrium from plenty of others beyond the party.
The campaign in Holborn and St Pancras might be over. The questions for Polanski certainly aren’t.