The seat became vacant this month when the former prime minister Keir Starmer announced he was leaving parliament.
Polanski has said the Greens, which made gains in the area in the local elections in May, are underdogs in the race but he is confident they can beat Labour, which won the seat with a majority of more than 11,000 at the 2024 general election.
On Wednesday, Labour selected the Camden council leader, Sagal Abdi-Wali, as its candidate. She said: “This place welcomed my family as refugees and gave us hope when we needed it most. I am so grateful to have had the opportunity to build a life here, serving our community as a councillor, school governor and community activist.”
Some in Labour are understood to be concerned about the impact of upcoming oil and gas announcements on the campaign. Industry insiders expect the government to greenlight the Jackdaw gasfield as soon as next week, but there are expectations that any announcement on Rosebank, a contentious oilfield, will be delayed until after the byelection.