Tens of thousands of people have taken to the streets of London to call for a permanent ceasefire in Gaza.

Police said 18 arrests were made over the course of the day, which came amid a temporary truce on a day that saw periods of uncertainty about the release of the next set of hostages.

Qatari and Egyptian mediators have said that Hamas has agreed to release 13 Israelis and seven foreign nationals in exchange for 39 Palestinians imprisoned by Israel.

It came after Hamas delayed the releases for several hours, saying Israel had violated the terms of a truce deal that had set the stage for such swaps.

The pause in the fighting follows weeks of Israeli bombardments of Gaza after the Hamas incursion into southern Israel that saw 1,200 people killed.

Protesters in London marched from Park Lane to Whitehall, with the Metropolitan Police handing out leaflets to provide “absolute clarity” on what will be deemed an offence.

It comes after weeks of pressure on the force over the handling of the now-regular demonstrations, with pressure from senior politicians for officers to come down harder on alleged displays of antisemitism.

Of the 18, the Met said that one man was arrested on suspicion of inciting racial hatred while another four were arrested on suspicion of distributing material likely to stir up racial hated.

Two men were also arrested on suspicion of supporting a proscribed organisation, after being seen wearing what the force called “green headbands with white Arabic script” that were “similar” to those worn by Hamas.

Deputy Assistant Commissioner Ade Adelekan said: “I would like to acknowledge the overwhelming majority who came into London today and exercised their right to protest lawfully.

“Regrettably, there was still a small minority who believed the law did not apply to them. Thanks to the efforts of our CCTV teams and other officers, a number of those are already in custody.

“Investigations into other offences are already under way and will continue in the coming days.

“I would also like to thank the Met officers, as well as all those from other forces who travelled long distances to help us keep London safe, for their efforts.

“We said we would intervene decisively where offences took place and that is what they did.”

Organisers Stop the War Coalition had asked anyone attending to avoid “any actions that might leave you or others around you open to arrest”.

“We ask that all attending our marches respect these clear anti-racist principles, including in any signs or placards they choose to bring to the march,” the group said in a statement.

During the march a series of handmade placards and banners were held up by pro-Palestinian demonstrators, with some referencing the slogan “from the river to the sea”.

One placard displayed a picture of Labour leader Sir Keir Starmer under the word “Genocide”, while another had a picture of leaders of the G7 above the phrase “War criminals on the run”.

Hundreds also gathered outside the Egyptian Embassy in Mayfair for a demonstration by Hizb-ut-Tahrir, in the first protest by the group since October 21 after a video emerged showing a man chanting “jihad”.

The Met said no offences were identified from the clip, but it prompted an outcry from politicians.

At the start of the rally on Saturday, the crowd was warned by an organiser: “Don’t come up with your own chants, follow what is on the stage, follow the chants from those who are chanting.”

Around 20 police officers were present at the peaceful demonstration which lasted approximately 90 minutes.

A statement by the group said Muslim leaders “should not feel bound” by Western laws and borders, calling the latter “mere lines in the sand”.

Dr Abdul Wahid, of the UK executive committee of Hizb-ut-Tahrir, told the crowd liberation would mean a “system that allowed Muslim, Jew and Christian to live side by side in peace and respect with everyone having rights”.

The crowd, made up of men, women and children, held signs that read “Muslim Armies! Liberate Palestine!” and “US & UK Hands Off The Middle East”.

Two women were later arrested for a racially aggravated public order offence after “holding placards with messaging on likely to cause harassment, alarm or distress”, the Met said.

A “breakaway group” from the main protest also marched up Whitehall after the demonstration had ended, with some setting off flares.

Six people were arrested for refusing directions to disperse under public order legislation, while the Met said one man was arrested near Trafalgar Square for alleged possession of an knife.

A 90-minute march organised by the charity Campaign Against Antisemitism is also due to take place on Sunday, with around 40,000-50,000 people expected to attend.

On the first day of the four-day ceasefire, Hamas released 24 of the about 240 hostages taken during its October 7 attack on Israel that triggered the war, and Israel freed 39 Palestinians from prison.

Those freed from captivity in Gaza were 13 Israelis, 10 Thai nationals and a citizen of the Philippines.

Under the agreement, Hamas will release one Israeli hostage for every three Palestinian prisoners freed.