Zack Polanski has apologised for sharing a social media post condemning the actions of police officers who arrested the suspect in the Golders Green attack.
The Green Party leader had reposted a message on X accusing officers of "repeatedly and violently kicking a mentally ill man in the head when he was already incapacitated by Taser".
In a statement on Friday, Polanski apologised for "sharing a tweet in haste", adding that he should not have commented on the police response via social media.
Sir Keir Starmer branded the decision to share the post "disgraceful", in a BBC interview recorded before Polanski's apology.
Speaking to BBC Radio 4's Today programme in an interview to be broadcast on Saturday, Sir Keir said he had met the officers involved in the arrest.
He added that in the circumstances, you could understand why the officers acted in the way that they did.
"There's a guy on the ground, he's got a rucksack on. And I don't know what was going through the mind of those officers, but if I was there, I'd be thinking, he's going to detonate something. He's going to blow me up and everybody around here," the prime minister added.
"In those circumstances, I think you can quite see why what could have gone through their mind is, we need to do whatever we can to disable this guy."
Polanski hit back at the PM's criticisms in a post on X, saying: "Today the prime minister uses his office to attack the only Jewish party leader to score political points."
Polanski's repost had also been criticised by Metropolitan Police Commissioner Sir Mark Rowley, who accused the Green leader of amplifying "inaccurate and misinformed commentary" in a letter published by the force.
In his statement, Polanski said he had invited Sir Mark to "meet with me to discuss the police response and the wider issues raised in his letter".
But he added: "Everyone in leadership has a responsibility for lowering the temperature at a time of such tension".
"Police responses to emergency situations such as these do need later reflection in the right forums, but I accept that social media is not the appropriate channel for doing so."
It is unusual for senior police leaders to publicly criticise politicians, and Sir Mark's letter comes at a time of heightened political sensitivity ahead of elections in Scotland, Wales and some English councils next week.
Speaking earlier, the Met chief denied his move marked an "intervention into politics", arguing it was legitimate for him to defend his officers in the face of public criticism from "somebody eminent".
"If someone wants to step onto my responsibilities of operational policing, I will deal with that assertively, like I did in this case," he added.
The Met has released footage from the officers' body-worn cameras, in which they can be heard shouting repeatedly for the suspect to "get down on the ground" before he is Tasered, and then "drop the knife".
It came after video shared on social media appeared to show the moment of the arrest, in which the officers can be seen kicking the man in the head several times in the struggle to wrest a knife from him.
Regarding the incident, a spokesperson from the Independent Office for Police Conduct said on Thursday evening: "We received a mandatory referral from the Met this afternoon, which relates to injuries reportedly sustained by the man who was arrested following yesterday's attacks in Golders Green."
Polanski, a member of the London Assembly, which has a role in overseeing the Met, became leader of the Green Party of England and Wales last September.
He had faced criticism for his repost from Anthony Slaughter, who leads the Greens in Wales, who said it seemed "inappropriate".
Green Party deputy leader Rachel Millward also appeared to distance herself from the comments on Thursday, praising the officers as "brave", and adding the incident would have been "beyond terrifying".
Multiple senior figures within the Greens are understood to have expressed concern about Polanski's decision to share the post criticising officers.
One source accused Polanski of an approach that fuels "culture wars".
"It is not how you win wider support," they said. "It is crucial that the leadership thinks about the direction it is taking the party in and who that is attracting."
The Liberal Democrats accused Polanski of making a "non-apology" and said he should disown the comments he reposted "in unambiguous terms".
The Metropolitan Police said on Friday it had received Polanski's letter, and would meet him after next week's elections.
Essa Suleiman, 45, has been charged with attempting to murder Shloime Rand, 34, and Moshe Shine, 76, in Golders Green on Wednesday morning.
It is also alleged Suleiman attempted to murder Ishmail Hussein in a knife attack at Hussein's flat in Southwark, south London, earlier on the same day. Hussein had known Suleiman for around 20 years.
He also faces a charge of possessing a knife in a public place in Golders Green.
He appeared in court earlier and stood to confirm his name and date of birth, but did not enter any pleas.
His case has been sent to the Old Bailey where he will next appear on 15 May for a preliminary hearing. He remains in custody.
