Confrontations broke out as police tried to move demonstrators from the Israeli embassy gates
Thousands of demonstrators have marched through London to call for an immediate ceasefire in the conflict in Gaza.
The protest started peacefully but there were confrontations as police tried to move demonstrators away from the gates of the Israeli embassy.
The windows of a Starbucks was smashed and three police officers were injured as a minority of people threw missiles.
The Metropolitan Police says 20,000 people marched but the BBC estimates the figure could be as high as 50,000.
It is estimated there were several hundred police officers dealing with around 200 protesters outside the embassy.
This group were being allowed to leave the cordon one at a time, some were being identified by police and are being taken away for questioning.
BBC correspondent Robert Hall said given the number of people involved, the protest had been peaceful.
"But as darkness fell a small number of people, several hundred, have begun confronting police and missiles have been thrown," he said.
"Although these are ugly and unwelcome scenes, they do not represent what has happened for most of the afternoon."
Metropolitan Police Commander Bob Broadhurst said: "We are very disappointed by the irresponsible actions of those who have challenged police by ripping apart security barriers and throwing objects at them.
"A hard core of demonstrators are undermining the cause of the vast majority of people on this demonstration, who are law-abiding citizens wishing to protest peacefully."
Approximately 15 people have been arrested, 12 for violent disorder; one for aggravated trespass; and two for assaulting a police officer.
The march was organised by groups including Stop the War Coalition, the British Muslim Initiative and the Palestine Solidarity Campaign.
Protests have also taken place in Edinburgh, Aberdeen, Belfast, Newcastle and Southampton.
There would have been outrage from governments around the world if this had happened anywhere else - the condemnation has been at best half-hearted
In Edinburgh around 300 shoes were thrown towards the US consulate by protesters and three police officers suffered minor injuries.
Celebrities including musicians Brian Eno and Annie Lennox joined the march.
Rallies were addressed by speakers including Eno, former London mayor Ken Livingstone and Cherie Blair's half-sister Lauren Booth.
Lindsey German, Stop the War's convenor, said: "We are calling for an end to the massacre and for Israel to get out of Gaza and Palestine.
"We want the British government to take a much stronger position. There would have been outrage from governments around the world if this had happened anywhere else - the condemnation has been at best half-hearted."
Former Mayor of London Ken Livingstone said in a statement: "The British government and European Union have the economic leverage to stop this carnage.
"They must take decisive action to force Israel to end the slaughter."
On Sunday, the Board of Deputies of British Jews will also hold a rally calling for peace in Israel and Gaza in Trafalgar Square.
The conflict in Gaza is entering its third week, despite international calls for a ceasefire.
Israel said it launched 40 overnight air strikes, while Hamas militants fired several rockets at Israeli towns.
Senior Palestinian officials are in Egypt for talks on how to end the conflict.
Health officials in Gaza say more than 800 Palestinians have died. Israel says 13 Israelis have been killed.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.