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Labour leader Ed Miliband addressed crowds in Hyde Park and the main march organised by the Trades Union Congress passed off peacefully.
But small groups attacked shops and banks with a stand-off in Piccadilly. There have been 214 arrests and 66 people injured, including 13 police.
Ministers say the cuts are necessary to get the public finances in order.
In the largest public protest since the Iraq war rally in 2003, marchers from across the UK set off from Victoria Embankment to Hyde Park, where TUC general secretary Brendan Barber was first in a line of speakers.
"We are here to send a message to the government that we are strong and united," he said.
"We will fight the savage cuts and we will not let them destroy peoples' services, jobs and lives."