Confrontation on Wednesday followed by further protests, which lead to more arrests and allegations of heavy-handed policing

Students were involved in a series of angry confrontations with the police in central London on Thursday as allegations circulated that officers had used unacceptable levels of force to break up campus protests over the past few weeks.

Video footage obtained by the Guardian appeared to show one officer striking a hooded protester in the face after students occupied part of the University of London Senate House headquarters on Wednesday.

On Thursday about 200 students held a "Cops off campus" rally outside the University of London Union building, which led to further violent confrontations with scores of officers that spread to surrounding streets. A Metropolitan police spokesman said there had been 36 arrests.

Michael Chessum, president of the University of London Union, said: "The level of police force that we have seen in the last couple of days is totally unprecedented on university campuses. It appears pre-planned. It is as if they are reacting to a riot situation – taking the level of force – and using it against students protesting on a university campus."

On Wednesday, demonstrators had occupied part of the University of London Senate House headquarters. Police and the university's private security staff broke up the demonstration and five protesters were arrested, with one held on suspicion of assaulting an officer.

Students claimed the police and private security staff had been unnecessarily violent and accused officers of assaulting them. Video footage seen by the Guardian appeared to show one officer striking a hooded protester in the face. In the footage, the demonstrator – who gave his name as Tee Jay – fell to the ground and the crowd was pushed back.

Jay, 24, from Hackney, north-east London, said: "Nothing was said. The police were trying to clear the crowd of people. I turned my back to [the police officer] to kind of walk away, he pushed, I kind of turned round to see who it was – 'Why are you pushing me?'

"The punch came and I went straight to the floor, then I got up and left." The University of West London media production student said he was part of the group that occupied an area of Senate House.

Another protester, Helen Singh, a philosophy student, claimed she was pushed over by officers, who were "punching people indiscriminately". "We were walking away from the protest. I was pushed to the ground and my glasses smashed into three pieces," she said.

A police spokesman said: "We have received no complaints in relation to police action at Wednesday's protest."

On Thursday, at a demonstration against police tactics, which had been organised before Wednesday's incident, about 200 demonstrators marched from the student union to Senate House.

When demonstrators arrived, there were skirmishes with police, who were already inside the premises. Several more police vans arrived and over the next two hours there were a series of clashes between small groups of protesters and police in the surrounding streets. Students again claimed the police had been heavy-handed.

Chessum said he thought the "unprecedented response" by the authorities was part of an attempt to stop the student protest movement gaining momentum.

"They know from 2010 [when there were large-scale student protests in London and around the country] that this sort of heavy-handed policing puts people off, and I think this is what they are trying to do this time."