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The clear-up after violent activists targeted central London following anti-cuts protests could cost "tens of thousands" of pounds, a council said.

Westminster Council said about 100 street cleaners worked until 0600 BST on Sunday to clean graffiti and litter.

Some activists clashed with police in Oxford Circus, Piccadilly and Trafalgar Square, after up to 500,000 people took part in a peaceful march to Hyde Park.

The 2012 clock, the memorial and the Ritz hotel were attacked.

Police arrested 201 people over the violence.

In December, Westminster Council spent £50,000 to clear-up the damage around Parliament Square following violent protests after MPs voted to raise tuition fees in England.

Saturday's anti-spending cuts march from Embankment to Hyde Park was organised by the TUC. The organisation has condemned the violence that followed the rally.

Violence erupted after some activists gathered in Oxford Circus, before spilling on to Piccadilly and finally converging in Trafalgar Square.

The group clashed with police until the early hours of the morning.

In a separate incident about 200 supporters of campaign group UK Uncut staged a sit-in at luxury Piccadilly store Fortnum & Mason.

A spokesman for the demonstrators said the store was chosen because part-owners Whittington Investments "dodge tens of millions in tax".

Westminster Council was responsible for clearing the streets in the West End and central London and restoring the historic square.

On a normal Saturday night 30 to 40 cleaners work in the area, but 100 street cleaners were working from 2200 GMT until 0600 BST on Sunday following the demonstrations, a council spokeswoman said.

Councillor Brian Connell, the council's cabinet member for business, said: "Its ironic and regrettable that a minority of people claiming to defend jobs are content to damage the livelihoods of the thousands employed in heart of the capital."

The Olympic Countdown Clock had paint and scratches on it, which its makers Omega described as "superficial damage".

The New West End Company, which represents retailers in the shopping area, said cleaners were at work overnight.

Most shops were expected to be open for business.

Kit Malthouse, chairman of the Metropolitan Police Authority, said: "I counted these anarchists myself.

"They were a nasty bunch of black-shirted thugs on Piccadilly and it was pretty obvious that they were intent on rampaging around and would be very difficult to control.

"There is a difficult balance because they were intermingling with, and were in amongst, getting on for 400,000 TUC protesters."

Stuart Jamieson, a 22-year-old student from Glasgow, wanted to do some sight-seeing before attending Scotland's match against Brazil at Emirates Stadium.

He said: "It's a total shame. We are tourists who have come to see the sights so it takes a wee bit away from the experience."

Correction 28 March 2011: An earlier version of this story did not state that the Fortnum & Mason protest was a separate incident. This has since been amended.