Keir Starmer has condemned Zack Polanski as “disgraceful” and unfit to head a political party after the Greens’ leader shared a social media post critical of the way police tackled the suspect in the Golders Green stabbings.

The prime minister said any criticism of the police involved in the arrest was unfair on officers having to make split-second decisions in a moment of potentially grave danger.

Police were filmed detaining the suspect after two Jewish people were stabbed in the north-west London suburb on Wednesday. Footage of the arrest shared on social media shows two officers appearing to kick the man on or near his head.

Polanski retweeted, without comment, a post on X alleging that officers were “repeatedly and violently kicking a mentally ill man in the head” when he was already incapacitated by a stun gun.

Speaking to BBC Radio 4, Starmer said that, having seen the footage, police might have believed an explosive device was in the rucksack carried by the suspect.

“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.’ And 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,’” Starmer said.

He added: “You have to make a decision in that split moment according to the situation as you understand it to be. And for politicians to wade in, as Zack Polanski did, is disgraceful. He’s not fit to lead any political party.”

Polanski yesterday apologised for the post, saying he shared it “in haste”.

Starmer’s intervention came after the Metropolitan police commissioner, Mark Rowley, wrote a letter to Polanski describing the claim as “inaccurate and misinformed commentary”. He praised the officers as “nothing short of extraordinary”, adding: “Without their efforts to stop him, I dread to think what the outcome could have been.”

Rowley later told the BBC that his letter was not an “intervention to politics”, adding: “I’m simply dealing with operational policing and defending my officers because I want them to have confidence to protect Londoners.

“Officers need confidence in confronting these dangerous people, and if an eminent person thoughtlessly steps into that and undermines that, then I’m going to deal with that.”

In other interviews on Friday, Rowley said his force would need more resources to protect Jewish communities, and that he was concerned about the possible scale of two protest marches planned in London during May.

Kemi Badenoch, the Conservative leader, said: “If someone Zack Polanski loved had just been stabbed, I don’t think he would be worried about how the police were disarming that person.”

In Polanski’s statement, issued on Friday afternoon, he apologised for the post, saying: “Everyone in leadership has a responsibility for lowering the temperature at a time of such tension, and I apologise for sharing a tweet in haste.

“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. I have invited Mark Rowley to meet with me to discuss the police response and the wider issues raised in his letter.’

He also said in a separate social media post that during a campaign visit to Hastings, East Sussex, a group of protesters directed Nazi salutes at him. He added: “Today the prime minister uses his office to attack the only Jewish party leader to score political points.”

The row came as the director of public prosecutions for England and Wales, Stephen Parkinson, promised to firmly tackle all hate crimes, warning of a “deeply troubling rise in antisemitic incidents across the country”.

In a statement on Friday, Parkinson said he recognised the “profound fear, distress and anger” that Jewish people were feeling, adding: “Antisemitic hate crime is not only an attack on individuals – it is an attack on the values of respect, tolerance and the rule of law that underpin our society.

“Let me be clear: those who commit antisemitic crimes will be held accountable. The Crown Prosecution Service will use the full force of the law to ensure those responsible are prosecuted robustly and swiftly, and justice is done.”

Essa Suleiman, 45, appeared in court on Friday charged with the attempted murders of three people during two knife attacks in London on Wednesday – the incident in Golders Green and an alleged attack during a personal dispute in south London.