Sir John Curtice has delivered his verdict on Zack Polanski’s chances of winning Sir Keir Starmer’s former seat and entering the House of Commons for the first time.The polling guru spoke out just days before polls open in Holborn & St Pancras on October 8.Mr Polanski, who received just 728 votes when he stood in the Cities of London & Westminster in 2019, is looking to build momentum after Andy Burnham handed Labour a poll boost when he became Prime Minister.Speaking at a Demos fringe event at the Green Party Conference on October 2, Sir John claimed Mr Polanski’s initial bounce as leader was now going in reverse.Looking ahead to polls opening next week, Sir John said: “If you look at what happened in the constituency on May 7 and you include in the Green vote the vote for the Camden Alliance candidates, which came out of Andrew Feinstein’s campaign, you were about four points behind Labour at the time.“Now, since then, Labour’s vote in the polls has gone up, yours has gone down.“So basically if you do succeed in winning the by-election, I’m not saying you won’t, but if you do succeed, it will be regarded as a very substantial shot at Westminster.”Labour is defending an 11,572-vote majority in Holborn & St Pancras, with new candidate Sagal Abdi-Wali looking to succeed Sir Keir as the local MP.Zack Polanski delivering his keynote speech at Green Party Conference | PAMeanwhile, pro-Gaza independent Andrew Feinstein and ex-Green candidate David Stansell amassed a combined total of 29.3 per cent in 2024.Mr Feinstein, who claimed Mr Polanski had asked him to stand on a joint ticket, stepped aside to give the Green leader a free run against Labour.Speaking while on the campaign trail, Mr Polanski said: “I think the seat is winnable, and I think it’s probably 50/50 right now. It’s really, really on a knife-edge.”Green Party members were even told they could get their conference tickets refunded if they wanted to help Mr Polanski’s in Holborn & St Pancras this weekend. But Sir John also raised questions over Mr Polanski’s standing with voters, suggesting his favourability had yet to fully recover from controversies earlier in the year.He said: “There clearly were some controversies about some of the debates that your leader got into at that point, and just the truth is recovering from that still seems to be a work in progress.”Sir Keir Starmer at his Holborn and St Pancras count | PAMr Polanski’s net approval rating fell from minus eight per cent earlier this year to minus 27 per cent last month.The drop came after Mr Polanski came under fire for sharing a post criticising Metropolitan Police officers who had detained the suspect in the Golders Green stabbing attack.Mr Polanski has also faced criticism over claims about his previous work and personal arrangements, including hypnotherapy to increase breast sizes and his failure to pay council tax while living on a houseboat.There has even been speculation that Mr Polanski could be forced to step aside as leader of the Green Party if he failed to win the seat on October 8.However, Mr Polanski rejected any suggestion he would resign and instead expressed some frustration about being asked the same question about his future. Zack Polanski has taken a swipe at Andy Burnham | PAAsked in an interview with the Guardian how much his position as leader depended on victory, Polanski said: “It doesn’t depend on it whatsoever.”Under the Green Party’s constitution, Mr Polanski could be forced into a fresh leadership contest if 10 per cent of party members sign a petition calling for his recall.Meanwhile, the party’s ruling Green Party Council can also recall him with a two-thirds majority.However, Sir John’s assessment of the Green Party’s prospects went beyond Mr Polanski’s showing in the Holborn & St Pancras by-election next week.Mr Polanski enjoyed a significant boost in the polls after taking over the party, with Green support reaching around 15 per cent in March.Sir John Curtice delivered his verdict at the Green Party Conference | GETTYBut Sir John said that initial surge had since gone into reverse, with support falling back to around 10 per cent.He also warned that the party’s electoral appeal remained concentrated among a relatively narrow section of the electorate.Sir John said: “Basically, the crucial point you need to understand is that you are appealing to a very, very much a niche market.“It’s young, socially liberal, somewhat left-wing, and relatively well-educated Britain. That’s your modal voter.“That inevitably puts you in competition with Labour and to some degree the Liberal Democrats.”However, Sir John suggested the Greens could still find themselves in a potentially influential position at Westminster if their support translated into a small group of MPs at the next general election.He said: “On the other hand, according to three of them, you could still potentially have a pivotal role in the next House of Commons if the election were to be now, which of course it’s not going to be because Labour plus the Liberal Democrats, according to three of these projections, do not get to 326.Andy Burnham saw off the threat from the Greens and Reform UK in Makerfield | GETTY“Whereas your somewhere between three and nine seats were potentially getting closer to the point where, given the position in Northern Ireland, a Labour minority government would be able to have control.“So you potentially are in a position of having leverage even if you’re not necessarily in a position where you might get seats.”The question of a potential deal with Labour could also become increasingly important as the Greens look towards the next general election.Mr Polanski categorically ruled out working with Sir Keir but said he could see the potential for a political partnership with Mr Burnham.“I could see the potential to work with Andy Burnham to stop Reform and to challenge the rise of the far-right,” Mr Polanski said earlier this year.“I would rule it out with Keir Starmer, but I wouldn’t rule it out with Burnham.”