A university student suspected of throwing a fire extinguisher at police during the Millbank riot was arrested tonight.
The 23-year-old man, a student at Anglia Ruskin University in Cambridge, was held by officers on suspicion of violent disorder.
Police said the man, who is originally from Reading, was being questioned at Parkside police station in Cambridge.
The suspect was identified as teams of officers scoured footage recorded as protesters stormed the building housing the Tory party headquarters on Wednesday.
Police Federation representatives have called for the person who flung the empty metal fire extinguisher to be charged with attempted murder.
Senior officers said it narrowly missed injuring two territorial support group officers, brushing down the back of one and hitting the knees of another.
The incident was one of the defining moments of the four-hour stand-off after a breakaway group of students attacked the Millbank office complex.
Up to 50 demonstrators smashed windows, discharged fire extinguishers and threw debris from the roof of the building.
But hundreds of others gathered in a forecourt below booed the culprit and shouted to others to stop damaging the building and throwing missiles.
Earlier today the Met said that 10 of the 54 people arrested during sprawling outbreaks of disorder were aged under 18.
A spokesman said most of the others were students, most aged between 18 and 26, and including 33 men and 21 women.
A Met spokesman said: "This arrest follows an investigation into public disorder where a fire extinguisher was thrown from the roof of Millbank Tower."
An Anglia Ruskin spokesman said: "We understand that one of our students was arrested earlier today in connection with the incident at Millbank Tower. We are co-operating fully with the police in their inquiries."
Some student activists began fighting a rearguard action today amid widespread condemnation of the violence and fears of further trouble on November 24.
It is widely believed that ministers will vote on the tuition fee rise in the Commons that day.
Clare Solomon, president of the University of London Union, claimed protesters were "goaded and provoked" by police.
She said: "I do not condone the violence towards people that perhaps might have happened on the day."
But she added: "When people were peacefully protesting, the police were hitting them with batons, and I have evidence of this.
"There were also people on the balconies, making hand gestures, rude hand gestures, shouting at them, jeering at them and I can understand why students felt totally provoked by this."
Meanwhile senior officials at the National Union of Students (NUS) wrote to staff at the Millbank Tower complex expressing "deep regret".
The email, signed by NUS president Aaron Porter and NUS chief executive Matt Hyde said: "We emphatically condemn these violent actions."
Tory peer Lord Tebbit hit out at the Goldsmiths, University of London lecturers who described the demonstration as "magnificent".
He said: "I can imagine what they would say were a group from the TaxPayers' Alliance to turn up at their homes and vandalise them in protest at the way these lecturers are leeching the taxpayer and failing to discipline their students."
Ann Widdecombe, the former Home Office minister, said that if the lecturers had used the word "magnificent" then "they are not fit for purpose".
Another ex-Tory MP and former deputy headmaster Harry Greenway, said the lecturers had behaved in a disgraceful way.
"They are not fit to hold their jobs or to receive the public money they are paid for that. If they are so supportive of these rioters, they should assist in paying for the damage."
Activist websites have published step-by-step instructions to those who fear they may be identified and arrested in the aftermath of the violence.
One anti-police site told participants to destroy potential evidence, including clothing and any distinctive jewellery worn.
A contributor urged demonstrators not to panic or give themselves up as a result of the flood of media coverage.
An internal inquiry into why police did not plan for violence, ordered by Met Commissioner Sir Paul Stephenson, is expected to be completed within days.
Senior officers are focusing on what intelligence was gathered before the protest and what resources were put in place.
The force planned to deploy just 225 officers to the protests, but had to double the numbers sent to the scene as trouble unfolded.
Prime Minister David Cameron has called for "the full force of the law" to be used against those responsible.
London mayor Boris Johnson said he hoped the small minority who were responsible "pay a serious price for their actions".
Students and staff were protesting against government plans to charge students up to £9,000 a year from 2012 - triple the current £3,290 fee.
Union leaders say the increase, and swingeing cuts to university budgets, will mean the end of affordable higher education.