Police are warning that this week's anti-fees protests could be hijacked by "violent youths".
Thousands of students and lecturers are expected to take to the streets on Wednesday and Thursday to demonstrate against the Government's plans to treble university tuition fees.
But the Metropolitan Police raised concerns that troublemakers could use the protests as an "excuse" for violence.
Protests held last month against the proposals were marred by violent clashes and resulted in numerous arrests.
Commander Bob Broadhurst, head of the Met's Public Order Branch said: "We have seen groups of youths descending on the last few student protests as the day progresses, purely with the aim of using the event as a venue for violence and to attack police.
"It has been obvious that these particular elements are not genuine protesters and they have no intention of protesting about cuts to tuition fees or any other issue. They have turned up purely to take part in violence and disorder.
"We will work with all protesters who want to peacefully protest and we acknowledge and respect their right to do so, but I would warn them to be aware of this violent element, which could harm them and their cause."
Mr Broadhurst called for parents to advise their children of the dangers of attending a protest as youngsters are more at risk if violence breaks out.
Many school children, including some dressed in school uniform, attended previous demonstrations, and the Met was criticised after pupils were "kettled" for several hours during the second of a series of protests on November 24.
"Violence and disorder is often a result of a minority who are determined to cause trouble," Mr Broadhurst said.
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