BBC: More than 250,000 people have attended a march and rally in central London against public spending cuts.
Labour leader Ed Miliband addressed crowds in Hyde Park and the main march organised by the Trades Union Congress passed off peacefully.
But splinter groups have attacked shops and banks, and a stand-off with police is taking place in Piccadilly. There have been 16 arrests.
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 Trades Union Congress 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."
Mr Barber was followed by Mr Miliband, who said: "The Tories said I should not come and speak today. But I am proud to stand with you. There is an alternative."
The march began at 1200 GMT and it took more than four hours for the protesters to file past the Houses of Parliament on their way to the park. (+ video) » | Saturday, March 26, 2011