Large demonstrations also took place in Dublin and Edinburgh, with a 70-year-old woman arrested and charged after a car ploughed into a small number of protesters.
Of these, three people were arrested on suspicion of showing support for a proscribed organisation, while three were arrested for inciting racial hatred, which related to “offensive placard” and chanting.
A further two arrests were made for racially aggravated public order offences while a ninth arrest was made for possession of stickers to be used for criminal damage.
Protesters had been warned that they faced police action if they “intentionally push the limit” on slogans and placards, with a number of arrests made in previous protests.
The demonstration comes after the UK and US carried out dozens of airstrikes against Houthi bases in Yemen.
The Iran-backed rebel group has repeatedly targeted commercial shipping in the Red Sea in the wake of Israel’s war against Hamas following the 7 October attack.
Protesters carried banners and placards saying: “Ceasefire now” and “End the siege”. Some were recorded seemingly chanting in favour of Yemen’s Houthi rebels, chanting: “Yemen, Yemen make us proud, turn another ship around.”
A number of conditions were in place for the march, the police said, with protesters not allowed to deviate from the route and speeches given a strict end time.
Home secretary James Cleverly said he had been briefed by the Met’s commissioner Sir Mark Rowley on plans to “ensure order and safety” during the protest.
“I back them to use their powers to manage the protest and crack down on any criminality,” the MP said.
Speaking at Parliament Square, Husam Zomlot, the Palestinian ambassador to the UK, accused the British government of “complicity” with Israel.
Mr Zomlot told the protesters Palestine was a “nation of freedom fighters”, saying: “I stand before you with a broken heart but not a broken spirit.”
He congratulated South Africa for bringing a genocide case against Israel at the UN’s International Court of Justice.
The seventh national march for Palestine also features an appearance by Little Amal, a giant puppet of a Syrian child refugee, which will join a group of Palestinian children.
The 3.5-metre puppet became an international symbol of human rights after she journeyed 8,000km from the Turkish-Syrian border to Manchester in July 2021.
The London march was one of several others being held in European cities including Paris, Rome, Milan where thousands also marched along the Irish capital’s main thoroughfare to protest Israel’s military operations in the Palestinian enclave.
During the march in Edinburgh, a 70-year-old woman was arrested and charged with a driving offence after her car ploughed into protesters, with no injuries reported.
In Dublin, a thousands-strong protest march reached the Irish Department of Foreign Affairs. Demonstrators waving Palestinian flags joined chants calling for the Irish government to support boycott, divestment and sanction actions and Israel.
Organisers also demanded that the Irish government support South Africa’s case against Israel at the International Court of Justice.
Ireland’s main opposition parties, including Sinn Fein, Labour and the Social Democrats, have called on the government to endorse South Africa’s action.
However, the Irish premier Leo Varadkar has said the government does not intend to join the case.
The Ireland-Palestine Solidarity Campaign, which organised the rally, said the demonstration was part of international day of action calling for an end to Israel’s operations in Gaza.
Protests were also held around the world, with demonstrations in South Africa’s Johannesburg, Indonesia’s Jakarta and Malaysia’s Kuala Lumpur.