Thousands of pro-Palestine protesters marched towards Whitehall from Russell Square in central London calling for an end to growing conflict in the Middle East.
Protesters waved Palestinian flags and chanted “free, free Palestine”, “occupation no more, Israel is a terrorist state” and “stop bombing Iran” on Saturday.
It comes after British foreign secretary David Lammy warned the situation in the Middle East was “perilous” and urged Iran to negotiate with the US.
Many chanted “shame on you” as they walked past dozens of counter-protesters, organised by pro-Israeli group Stop The Hate, near Waterloo Bridge.
At one point, police officers chased a suspect down the Strand and arrested them after a bottle was thrown at the group of counter-protesters.
Mr Lammy flew from Washington to Geneva, Switzerland, on Friday to meet Iranian foreign minister Abbas Araghchi alongside his French and German counterparts.
Speaking after the meeting, Mr Lammy told reporters: “It is still clear to me, as President Trump indicated yesterday, that there is a window of within two weeks where we can see a diplomatic solution.”
Urging Iran to “take that off ramp” and talk to the Americans, he said: “We have a window of time. This is perilous and deadly serious.”
He added that the US and Europe were pushing for Iran to agree to zero enrichment of uranium as a “starting point” for negotiations.
But Mr Araghchi said Iran would not negotiate with the US as long as Israel continued to carry out airstrikes against the country, and insisted his country’s nuclear programme was entirely peaceful.
The talks followed US president Donald Trump’s announcement that he would delay a decision on joining Israeli strikes against Iran for up to two weeks.
Both sides continued to exchange fire on Friday, with Iranian missiles targeting the city of Haifa while Israeli prime minister Benjamin Netanyahu said Tel Aviv’s military operation would continue “for as long as it takes”.
The Gaza war was triggered when Palestinian Hamas militants attacked Israel on October 7, 2023, killing 1,200 people and taking 251 hostages, according to Israeli tallies.
Israel’s subsequent military assault on Gaza has killed nearly 55,600 Palestinians, according to Gaza’s health ministry, while displacing almost the entire population of more than two million people and causing a hunger crisis.
