Video: Students dig in as police warn of violence on fees protests

As student sit-ins continue in Leeds, Bradford and Sheffield, thousands of students and lecturers are expected to take to the streets tomorrow 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.

"Police officers will endeavour to assist young and vulnerable people as much as they can if violence breaks out during a protest, but there is only so much they can do once they are in a crowd of thousands."

Protests are set to take place across the country as MPs gear up for Thursday's controversial vote on plans to charge students up to 9,000 per year in fees.

The National Union of Students (NUS) and the University and College Union (UCU) have announced that peaceful protests will be held at universities across the country tomorrow, and there will be a mass lobby of MPs on the day of the vote, followed by a rally in Westminster, they said.

A candlelit vigil will be held during the evening with 9,000 candles representing the potential new fee level.

Three days of national action have already been held in protest at the Government's plans.

The first, organised by UCU and NUS descended into chaos when a small group of activists stormed into Tory Party headquarters at 30 Millbank, lighting fires, breaking windows and throwing missiles.

The two unions later distanced themselves from the violence.

A fortnight later, on November 24, tens of thousands of people took part in marches, occupations and sit-ins around the country.

But Westminster bore the brunt of lawlessness as a small number of protesters were arrested for offences including violent disorder, theft and criminal damage.

The clashes centred around a stranded police van that was ransacked and looted a short distance from the entrance to Downing Street, and police were forced to "kettle" hundreds of protesters for around four hours a short distance from the Houses of Parliament.

Last week, shops were attacked, missiles thrown at police and fires lit at the base of Nelson's Column during a third day of protests.

The London landmark was also vandalised, with the words "revolution" and "no cuts" as well as expletives daubed on the plinth.