Thousands of students and activists are marching through central London to protest rising tuition fees.
More than 4,000 officers have been put on duty around Wednesday's demonstration - the largest number of police to hit the streets since August's riots.
Scotland Yard has estimated that 2,000 protesters are taking part in the march, while the organisers of the protest put the figure closer to 10,000.
In the City protesters are being tightly controlled by police lines as they make their way along their planned route. The demonstration is being held by police near Moorgate in London's financial district.
The protesters are to be allowed to stay at the rally point for two hours before being dispersed.
Further west several protesters had set up tents in Trafalgar Square, but police moved in to clear them out. Several arrests have been made.
Demonstrators in the Square were chanting "no democracy, no peace" and handing out copies of the newspaper - "one year on students march again".
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See below for a map of the route protesters are taking:
View Tuition Fee Protest in a larger map
Police are aiming to prevent a repeat of last year's fees protest when Conservative Party headquarters in Millbank was attacked. Only 225 officers policed the demonstrations and the Met are taking extra precautions after anarchists threatened to turn the peaceful rally into a "sea of rage".
On Tuesday, Scotland Yard announced rubber bullets would be "available" for use in cases of "extreme disorder".
One student told the Huffington Post UK ahead of the march that he did "not object to violence".
Mike Shaw, 20, said: "I'm going to protest peacefully but I don't think protestors being violent damages the cause. It does shine a bad light on the protest, yes, but if people want to smash a few windows then... We only got the attention of the press and government last year because of attacks at Millbank."
The Edinburgh University student is heading down to the capital on an overnight coach, along with 150 other protestors.
"Most of the violence is coming from the police which is what I am afraid will happen tomorrow. The announcement of police threatening us with plastic bullets - all that serves to do is heighten tension and keep people away who would usually have attended."