Scotland Yard has sent letters to young activists to warn them off attending Wednesday's student demonstration in London, as reports suggested police were considering using rubber bullets.
The letters are said to have been sent to anyone charged with a public disorder offence, even if they have not been prosecuted.
"It is in the public and your own interest that you do not involve yourself in any type of criminal or anti-social behaviour," the letter says.
"We have a responsibility to deliver a safe protest which protects residents, tourists, commuters, protesters and the wider community.
"Should you do so we will at the earliest opportunity arrest and place you before the court.
The University of London Union and the National Campaign Against Fees and Cuts are due to march through the the financial centre of London tomorrow culminating with a rally at 3.30pm.
Previous student demonstrations against a rise in tuition fees have been marred by violence, including one incident where protesters smashed their way into the Conservative Party's Wesminster headquarters.
The Metropolitan police has indicated that it is prepared to use rubber bullets in cases of "extreme" disorder, which would be the first time they have been fired outside of Northern Ireland.
More than 4,000 police are preparing to take to the streets to ensure public order.
David Cameron has said the decision as to whether to use rubber bullets or not was up to the police.
Appearing before the liaison committee in the Commons this afternoon he said: "I think these are matters for the police operationally to take. What I said at the time of the disturbances in August was it was right for politicians to discuss these issues with the police and the police to feel they have political backing."
He added: "The operational decisions must be for them to take."
The student demonstration tomorrow is expected to link up with the Occupy London protest which is encamped outside St Paul's Cathedral.
The prime minister criticised these protesters for establishing a permanent presence.
"The idea of establishing tents in the middle of a city I don't feel is particularly constructive," he said. "I don't think its particularly consturivet in Parliament Square or outside St Paul's."
The prime minister said he held the "rather quaint view" people should not be able to pitch tents wherever they liked.
"Protest is something you should do on two feet rather than lying down," he added. "In some cases in a rather comatose state."Suggest a correction