Pro Palestinian protests were held across the UK on Saturday despite a call from Prime Minister Keir Starmer to cancel them, two days after a deadly car-ramming and knife attack on a synagogue in Manchester.

Four people, two men and two women, remained in custody on suspicion of terrorism-related offences following Thursday’s attack. Police said an 18-year-old woman and a 43-year-old man who had been held earlier were released without further action.

Two people were killed and three others seriously injured in the attack on Yom Kippur, the holiest day of the Jewish calendar. The attack took place at the Heaton Park Hebrew Congregation Synagogue in north Manchester.

Police said they shot dead the assailant, 35-year-old UK citizen of Syrian descent Jihad Al-Shamie, within minutes of the alarm being raised.

The attack has caused concern within Britain’s Jewish community. Police said they were patrolling places of worship across Manchester “with a particular focus on providing a high-visibility presence within our Jewish communities”.

The Manchester synagogue attack was one of the worst anti-Semitic incidents in Europe since the October 7th, 2023, Hamas-led assault in Israel. The Hamas attack killed 1,219 people, mostly civilians, according to an AFP tally of Israeli official figures.

Israel’s military response in Gaza has killed at least 66,288 Palestinians, also mostly civilians, according to health ministry figures in the territory that the United Nations considers reliable.

The conflict has led to frequent pro-Palestinian rallies in Britain, which some critics allege have fuelled anti-Semitism.

Around 1,000 people gathered in Trafalgar Square in central London on Saturday to show support for the banned group Palestine Action, according to organisers Defend Our Juries.

A spokesperson said the group “stood in solidarity” with the Jewish community over the Manchester attack, adding, “Cancelling peaceful protests lets terror win.”

A smaller protest organised by Greater Manchester Friends of Palestine drew about 100 people in Manchester.

Ahead of the demonstrations, Prime Minister Starmer urged protesters not to join the rallies.

On X he said: “I urge anyone thinking about protesting this weekend to recognise and respect the grief of British Jews. This is a moment of mourning. It is not a time to stoke tension and cause further pain.”

Police said 488 people were arrested at the London protest “for supporting a proscribed organisation”. The oldest person arrested was 89.

Four people were detained for other offences. The Met Police said 297 remained in custody while the rest had been bailed.

Supporting the group has been a criminal offence under the Terrorism Act 2000 since the government banned it in early July. Hundreds of people have since been arrested at various demonstrations.

He said: “I’m ready to be arrested,” a 21-year-old student who did not want to be named told AFP. “The ban of Palestine Action is undemocratic. It shouldn’t be a terrorist group, they haven’t killed anybody.”

David Cannon, 73, chair of the Jewish Network for Palestine, said the demonstration was “totally separate” from what had happened in Manchester.

“There’s nothing Jewish about genocide, about apartheid, about ethnic cleansing,” he said.

The UK police watchdog said it would investigate the police shooting of attacker Al-Shamie.

The Independent Office for Police Conduct (IOPC) said its probe would also look into the deaths of two other people — one of whom died from a gunshot wound — and another person who was shot but survived.

The IOPC said there was no evidence anyone other than police officers had used firearms at the scene, suggesting both victims were accidentally shot by armed officers while they tackled Al-Shamie.

The IOPC said: “Our independent investigation will look at circumstances surrounding the fatal police shooting of Jihad Al-Shamie. A post mortem has today (Friday) concluded another man who died at the scene suffered a fatal gunshot wound.”