More than 180 people have been arrested by police investigating rioting during the series of protests against rising student tuition fees.
Senior officers said the vast majority of the 182 suspects were aged between 17 and 25 and have never been involved in violence or criminal acts before.
Detective Chief Superintendent Matt Horne, who is leading the inquiry, said he expects the figure to grow considerably as 80 officers comb through video footage.
Speaking at New Scotland Yard today, where protesters were expected to attempt to "kettle" police later, he said the inquiry could take months to complete.
He said: "182 individuals have now been arrested as a result of the four demonstrations and we anticipate that number to grow significantly.
"What struck me is the number of people arrested who did not go that day with necessarily any intention of committing any violent action."
Mr Horne said there was a "stark contrast" between scenes in Westminster and homes with crying parents and shocked young people when police turn up.
He added: "I would urge those who turn up for protests to think about the impact this could have on their future careers.
"When they are shown footage of their actions that day some are shocked by the impact of their behaviour."
Met Police Commissioner Sir Paul Stephenson said the cost of policing the demonstrations is significant and he has been "stripping London out" to meet the demand.
The senior officer said almost 3,000 officers were deployed last Thursday and he was proud of their professionalism in the face of unprecedented provocation and violence.
Sir Paul also said:
:: The Met ruled out using water cannon three years ago but is taking advice from colleagues in Northern Ireland about whether it could be used in London.
:: A report by Commander Ian Quinton into the attack on the royal car in Regent Street will be completed by Friday and handed to the Home Secretary.
:: The actions of mounted colleagues during protests was "absolutely splendid" and they are part of the "proud tradition" of British policing.
:: Senior officers will consider applying to the Home Secretary to ban forthcoming marches if necessary and if it will not inflame the situation further.
:: He will be absent from office for up to six weeks as he undergoes pre-planned surgery for what is believed to be a non-cancerous tumour in his femur.
Speaking about the protests, Sir Paul said a senior colleague reported that last Thursday saw the most "sustained and serious level of violence" in his 27-year career.
He said: "There were people who came absolutely prepared to commit a level of violence that day and to try and breach police lines.
"We have got to make sure that not only do we have a significant post-incident investigation but we are determined to bring those responsible to justice.
"There has been a lot of commentary about how we can prevent people intent on violence getting to these demonstrations.
"I would invite you to look at some of the people that have been arrested. Did they particularly stand out?
"Did some of the people on television screens look like they have some sort of tattoo on their foreheads saying 'I'm an extremist intent on committing violent crime?'
"We have not seen this level of violence in public demonstrations for many years so our tactics must adapt and we have got to keep reviewing and planning to achieve what is our duty to achieve."
Sir Paul said the idea police can stop all people intent on committing violence and criminal damage at protests is "frankly nonsense".
He added that he does not shrink from his responsibilities but said it would be "something of an understatement" to say protests are stretching the force.
Sir Paul said: "When you are putting 3,000 people out, not just on one day but a significant number of days, the consequences of that for the rest of the organisation are quite clear."
The senior officer added that he is "very worried" about the knock-on effect on securing neighbourhoods and town centres as police are drawn into the centre.
Speaking about changing police tactics at demonstrations, Sir Paul said he did not want to see a "paramilitary model" of policing in Britain.
He said: "We have seen the way a number of jurisdictions deal with public order and public disorder. That is a matter for them but we have seen the consequences across the world."
Sir Paul dismissed rumours of a split among senior Scotland Yard officers on water cannons as "spurious nonsense" and said a fresh review was taking place.
He said: "I am yet to be convinced that water cannon would be effective in our context. The only place it has been used is Northern Ireland and that is different.
"I do not want to engage in an arms race, a knee jerk reaction to thugs and hooligans who do not know how to behave when they are accompanied by an overwhelming number who want to demonstrate peacefully."
Sir Paul said a review and test undertaken three years ago, with the consent of the Police Authority, found it was not a good investment and unsuitable.
He added: "It is absolutely right that we should continue to review tactics and equipment in the light of developments.
"I am most reluctant to move towards this but at the same time we should keep everything under review."
Sir Paul said banning forthcoming marches was "one of the options we have got" but said it was a complicated approach and could spark more trouble.
Police can ask the Home Secretary to ban marches under the Public Order Act. They cannot ban demonstrations but can place conditions on them.
Sir Paul said: "When you have got people willing to break the law in this way, what is the likelihood of them obeying an order not to march or complying with conditions on a demonstration?
"Sometimes putting that power in could just be inflaming the situation further."
He said police may also consider boarding up potential targets for damage and public monuments such as the Cenotaph.
He declined to comment on whether colleagues would consider "snatch squads" to step in and arrest the most serious troublemakers.
Sir Paul would not say if any of the 182 people arrested by police were held in connection with the attack on the Royal car last Thursday evening.
He said Mr Quinton, who is seconded to the Home Office's security directorate, would report back on Friday, although his findings were likely to remain secret.
Asked if he considered resigning, Sir Paul said: "Any Commissioner at all times always considers what their position should be on any given incident and certain serious incidents.
"I am not going to go into any detail and certainly not comment publicly on any private discussions."
Asked why an outside force had not been brought in to conduct a review, Sir Paul replied: "We need to make a judgment on each individual circumstance."
Sir Paul added that the senior officers responsible for the security surrounding royals and VIPs should not have to fear the "sword of Damocles" every time they make a decision.
He said police aspire to be right "100% of the time" but this was not always possible and security teams were there precisely because of the risk some people face.Reuse content