More than 200,000 people took part in a demonstration in central London demanding an immediate ceasefire in Gaza, the Guardian reported.
The demonstration, organized by the Palestine Solidarity Campaign, Stop the War and the Campaign for Nuclear Disarmament, featured speeches from former Labor leader Jeremy Corbyn and The Crown actor Khalid Abdallah, among others.
A man has been arrested on suspicion of a terrorism-related offense in connection with soliciting support for a banned organisation, the Metropolitan Police said. The man was taken to a central London police station and remains in custody.
Three more arrests were made - of one person on suspicion of a racially motivated crime against public order and of two others on suspicion of causing harassment, alarm and disturbance.
Corbyn criticized the UK government for continuing the "horrible, sinister arms trade with Israel".
"What we're watching on world television in real time is the destruction of life, the wanton destruction of life in Gaza. And our governments still can't bring themselves to say the words 'permanent ceasefire', still can't threaten to stop the appalling arms trade with Israel and the supply of weapons from factories in France, Germany, Britain and the US that are killing people in Gaza," the former Labor leader said.
Abdallah, 43, who played Dodi Fayed in the Netflix series The Crown, said he attended a pro-Palestinian protest and took his children with him.
"I don't dream of a world where in 20, let alone 40 years, my children will be standing here in Trafalgar Square demanding justice for the Palestinians, demanding an end to the occupation. We cannot allow this to continue for another generation," said the actor.
Diane Abbott, MP for Hackney North and Stoke Newington, accused British politicians of "paying lip service" to a ceasefire.
The protest was held on the anniversary of Land Day, which commemorates the events that took place on March 30, 1976, when six Palestinians were killed in protest against Israel's land policy.
Thousands of Palestinians in Israel marked Land Day on March 29, calling for an end to the assault on Gaza.
The protesters, led by Arab members of Israel's parliament, marched through the northern city of Deir Hana, waving Palestinian flags and carrying placards reading: "Stop the war on Gaza."
The rally was joined by a smaller contingent of Israeli Jews, some of whom carried placards reading: "Jews and Arabs refuse to be enemies."
Since the war broke out almost six months ago, Arab citizens of Israel say they have experienced increasing hostility from the government and from other Israelis.
In Tel Aviv, thousands of Israelis also demonstrated on March 30 to call for the release of hostages held in Gaza and to show their displeasure with Benjamin Netanyahu's government.
Protesters lit fires and used trucks to block traffic, calling for the Israeli prime minister to resign. The police declared that the demonstration was illegal and called the protesters "rebels"./BGNES