More than 10,000 people took part in a demonstration in London on Saturday against Israel's offensive in the Gaza Strip, dpa reported.
Some of the protestors threw shoes at police, burned placards and tried to break through barriers.
Police said 12,000 people took part in the march from Hyde Park to the Israeli embassy, while media reports spoke of tens of thousands.
Protests also took place in Belfast, Edinburgh, Aberdeen and Newcastle.
Jewish organizations plan to hold peace demonstrations in London on Sunday.
London's former mayor Ken Livingstone, musician Brian Eno and singer Annie Lennox were among those who supported the protest Saturday.
Livingstone said the British government and the European Union should push Israel to "stop the carnage."
Over the last week, thousands in various British cities have been protesting the conflict, hurling shoes at the iron gates in front of Downing Street.
Shoe-throwing as a form of protest has gained popularity since an Iraqi journalist made headlines for throwing his shoes at US President George W Bush in mid-December.