Foreign Secretary Ed Miliband led Labour‘s first campaign to win a crunch by-election in London against Green leader Zack Polanski.

Mr Miliband rallied Labour activists in Holborn and St Pancras to “win back progressive voters” who had deserted the party to the Greens and other parties.

Hailing the upbeat tone struck by new Prime Minister Andy Burnham, compared to Sir Keir Starmer’s government, Mr Miliband stressed that “hope is in the air”.

Labour MPs from across London joined the weekend campaigning after Mr Polanski’s party was first out of the blocks in the key by-election.

They included Liam Conlon, MP for Beckenham and Penge, Tulip Siddiq, MP for Hampstead and Highgate, Deirdre Costigan, MP for Ealing Southall, Danny Beales, MP for Uxbridge and South Ruislip. Brent East MP Dawn Butler, Enfield North MP Feryal Clark and Feltham and Heston MP Seema Malhotra.

Mr Miliband, MP for Doncaster North but who grew up in north London, told Labour campaigners: “Hope is in the air, and I think we can go out in this by-election and really talk with pride about what Andy's new Government is doing.

“He has a big argument about how the country needs to change.

“Now it's up to us in Holborn and St Pancras to win back the progressive voters.”

The Standard revealed last week that Mr Polanski was set to stand for the Greens in the crunch by-election.

His selection still needs to be rubber-stamped by the local Green party.

But he was out campaigning in the constituency very shortly after Sir Keir Starmer announced tht he was standing down as the local MP, triggering the by-election.

The Greens intend to flood the constituency with activists, as they did in the Gorton and Denton by-election and were out in force on Sunday.

Mr Polanski said: “I knew today (Sunday) was going to be big. I didn’t know we’d have so many volunteers that we’d leaflet the ENTIRE constituency in just two hours (!!) - 80,000 leaflets.

“And we got to speak to so many people on their doorsteps. This is how we win this campaign.”

The Greens will also put up hundreds of poster boards as they try to persuade people to vote for the party for the first time.

The poster boards aim to signal to individuals who may be considering voting Green for the first time that other people in their street or neighbourhood are planning to do so.

Labour is yet to select its candidate for the by-election which is expected to take place in October.

Shortlisting interviews were due to take place on Monday before final hustings and selection meetings on Wednesday.

The frontrunner to be the party’s candidate is Sagal Abdi-Wali, a former child refugee and the leader of Camden Council.

Reform UK’s home affairs spokesman Zia Yusuf was slammed at the weekend after he posted on X: “The front runner being foisted on the people of Holborn by Labour to replace the former Prime Minister Keir Starmer in our Parliament was born in Somalia.

“Do you understand what’s happening?”

Business Secretary Jonathan Reynolds led condemnation of the remark, branding it “pretty straightforward racism”.

Mr Yusuf insists he did not mention race.

Mr Polanski has been seeking to talk up his links to the constituency.

“For too long now it’s been held back by governments who have failed to make the changes to improve people’s lives,” he said as he announced he would stand in the by-election.

“We know that the Greens can win here, and by electing me, voters will have someone who will always fight their corner – never scared of big donors or the party whip.”

Labour won the London seat with a majority, of 11,572 at the 2024 general election.

Sir Keir gained 18,884 votes, with the Greens trailing in third place with 4,030.

Independent candidate Andrew Feinstein gained 7,312 votes and came second and he has hinted at a willingness to do a deal with the Greens to deny Labour victory.

Political analysts believe the contest between Labour and the Greens could be close.