Police must prepare for more lawless demonstrations because the "game has changed", Britain's most senior officer has said.
Sir Paul Stephenson said his officers failed to correctly assess the mood of protesters in a new political climate before the Millbank riot two weeks ago.
But the Metropolitan Police boss said they did not make that mistake on Wednesday as clashes once again marred a mass march against rising student tuition fees.
The London force deployed more than 800 officers, almost four times as many as on November 10, as police prepared for a fresh wave of violence and disorder. Potential targets for occupation, including the headquarters of the Liberal Democrats, were encircled by officers as reserves surrounded Trafalgar Square.
Speaking at a meeting of the Metropolitan Police Authority (MPA) at City Hall, Sir Paul said the "likelihood is for more disorder on our streets".
He said: "We have been going through a period where we have not seen that sort of violent disorder. We had dealt with student organisers before and I think we based it too much on history. If we follow an intelligence-based model that stops you doing that. Obviously you realise the game has changed. Regrettably, the game has changed and we must act."
The senior officer defended the decision to "kettle" thousands of protesters, including many school pupils, in Whitehall, close to the entrance to Downing Street. He said when several large-scale marches linked up in Whitehall police wanted to stop them getting into Parliament Square and beyond.
The meeting heard a smaller group of known troublemakers tried and failed to target the Lib Dem Cowley Street headquarters earlier in the day.
Sir Paul said in recent years the Met has been reducing the numbers of officers and other resources deployed to tackle demonstrations. He said: "Regrettably we are going to have to review that. We are going to have to take a more cautious approach."
Speaking about the clashes on Wednesday, Sir Paul said: "The bottom line is we did not get it right two weeks ago and in my opinion we did get it right this time. We did put an enormous amount more assets out on Wednesday but we did get it right."