During the march, protesters learned that the conflict had escalated with Israeli ground troops entering Gaza, the BBC reported.
Other demonstrations were held around the world, including Athens, Berlin, Rome and Paris, and in smaller cities in Britain. Muslim Israelis held a large rally in Sakhnin in northern Israel.
In London, protesters marched to Trafalgar Square, where speakers included former Mayor Ken Livingstone. At Downing Street, the official residence and office of Prime Minister Gordon Brown, marchers threw about 1,000 shoes at the gates, echoing the action of an Iraqi journalist who threw his shoes at U.S. President George Bush at a news conference in Baghdad last month.
"The silence of the British government, and most Western governments, is obscene, and I think Gordon Brown will see this and recognize the real anger amongst Londoners," Livingstone told the BBC.
A breakaway group had a confrontation with police in Kensington as protesters attempted to reach the Israeli embassy. About 15 people were arrested.