The home secretary has told the Commons she does not think "anyone wants to see water cannon" used in Britain to quell disorder.
Theresa May was answering questions on last Thursday's violence around central London.
What began as a student protest of 3,000 swelled to at least 15,000 people, she said, some of them "street gangs and organised thugs".
May said "a significant number" were troublemakers intent on violence and some students "behaved appalingly".
She said it is "as ridiculous as it is unfair" to blame police tactics when some came armed with snooker balls, flares and other projectiles with the intention of attacking officers.
More than 2,800 Met police officers were deployed last Thursday and six were hospitalised.
May confirmed there was "physical contact" between a protester and the Duchess of Cornwall after the car carrying the Prince of Wales and the Duchess was surrounded by an angry mob.
A review of Royal security is expected to be completed by Friday but much of it will remain out of the public domain, she told the House.
May said 35 people have been arrested so far, but she expects the number to rise "significantly".
She added there has been a good public response to the publicaton of pictures of 14 people alleged to be the ringleaders of the violence and the Met will be publishing more.
May said she is determined to maintain the right to protest and the British model of policing by consent.
Shadow home secretary Ed Balls praised the police's bravery, commitment and restraint, but said lessons must be learnt, especially on the containment of protesters.
He called the attack on the Royal car "cowardly and despicable" and urged May to shelve a cost-cutting review of protection for the Royals.
Balls blamed Thursday's violence on a "small minority" who hijacked an entirely legitimate protest about student fees and EMA.
He asked if police commissioners, new elected posts planned by the government, will have the power to introduce water cannon or rubber bullets to deal with disorder.
May replied that the home office sets the legal parameters on what methods or equipment police can use and no-one has suggested plastic bullets.
Water cannon has not been authorised for use in Britain, she told MPs.
May said under police commissioners, chief constables will maintain operational independence. She said in her opinion water cannon is not needed in Britain.
Ian Paisley (DUP, Antrim North) claimed that a request to the PSNI for two of their six water cannons to be sent to London's police force has already been received.
May said while all options must be looked at, the home office has not authorised the use of water cannon.
Former Northern Ireland office minister Paul Goggins (Lab, Wythenshawe and Sale East) said he would not rule out the use of water cannon.
David Rutley (Con, Macclesfield) condemned privileged people, "privately and expensively eductated", who attacked the Cenotaph.
May agreed and said those people will face the full force of the law. She added that desecration of the Cenotaph contrasts with the bravery of British troops serving in conflict zones.
David Blunkett (Lab, Sheffield Brightside) questioned the reported "lapse of intelligence and communication" by Royal protection officers.
May said the review would consider those issues.


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