A car containing Prince Charles and the Duchess of Cornwall has been attacked amid violence after MPs voted to raise university tuition fees in England.
A window was cracked and their car hit by paint, but the couple were unharmed.
In angry scenes, protesters battled with police in Parliament Square. Hundreds were contained on Westminster Bridge for a time by officers.
Police say 12 officers and 43 protesters have been injured, while 34 arrests were made.
Prime Minister David Cameron said it was "shocking and regrettable" that protesters had attacked the prince's car.
Clarence House said the royal couple were safe and attended the Royal Variety performance as scheduled.
Metropolitan Police Commissioner Sir Paul Stephenson said there would be a "very serious and very detailed investigation" into the disturbances, in which 10 police officers have been injured.
The vote will mean fees will almost treble to £9,000 a year. The government's majority was cut by three-quarters to 21 in a backbench rebellion. Three ministerial aides resigned.
Only 28 Lib Dem MPs - less than half - voted for the government's plans for tuition fees. Six Conservative MPs voted against.
There were angry clashes as protesters - some throwing missiles - fought to break through police lines.
Riot police had to force back protesters who were smashing windows of the Treasury and the Supreme Court.
Earlier, protesters had largely taken over Parliament Square and pressed against lines of police in front of the Houses of Parliament.
Mounted police were used to control crowds, at one point charging a group of protesters, as thousands of demonstrators protested outside the Houses of Parliament.
Other reported actions taken by the protesters include:
- Setting the Christmas tree in Trafalgar Square alight
- Smashing windows at shops in Oxford Street
- Vandalising statues in Parliament Square, including that of Winston Churchill
- A sit-in by about 150 students at the National Gallery
Superintendent Julia Pendry said officers had come under sustained attack and condemned "acts of wanton vandalism, wanton violence" by protesters.
In violent scenes earlier, the BBC's Mark Georgiou said there had been injuries to both police and protesters near to Westminster Abbey.
The Metropolitan Police said there were attacks using "flares, sticks, snooker balls and paint balls".
Home Secretary Theresa May said she "utterly condemned" the violence.
"What we are seeing in London tonight, the wanton vandalism, smashing of windows, has nothing to do with peaceful protest," she said.
"I have spoken to Paul Stephenson, the Met Commissioner, and he has updated me on the appalling levels of violence seen today.
"Attacks on police officers and property show that some of the protesters have no respect for London or its citizens."
Students from around the UK gathered in London for a day of protests and a rally - with police expecting about 20,000 demonstrators.
The coalition government faced its first major backbench rebellion in the vote.
The BBC's Ben Brown, outside Parliament, said protesters shouted "shame on you" as news of the result filtered out to the crowd.
The package of measures will see fees rising to an upper limit of £9,000 per year - with requirements for universities to protect access for poorer students if they charge more than £6,000 per year.