Footage showing alleged police brutality at a memorial event for Ian Tomlinson led to the suspension last night of a second police officer.

Shot the day after the main 1 April demonstrations, it shows an incident during which frontline police were attempting to contain protesters who had gathered at the Bank of England for the vigil.

The 47-year-old newspaper vendor had collapsed and died nearby the previous night, and demonstrators had come dressed in black to lay flowers and demand answers about his death. At the time protesters were not aware of footage showing Tomlinson being attacked from behind by an officer before he collapsed.

The film begins showing hundreds of protesters gathered opposite the Royal Exchange. They are surrounded by lines of police who appeared to have formed a cordon, or "kettle", to contain them.

A man holding a newspaper attempts to leave the police cordon. He is seen remonstrating with police, who refuse to let him out. The crowd reacts angrily when minor scuffles break out between the man and police.

It is at this point that a short woman standing outside the cordon reacts angrily toward police. Her identity is not known. Photographs taken at precisely the same time show her clutching a digital camera and carton of orange juice. Swearing, she directs her anger at one particular officer.

The officer, who has concealed his badge numbers, appears to shove her back, saying: "Move back." She replies: "[I'm a] fucking woman."

The officer then appears to slap her across the face with the back of his hand, saying: "Go away." The footage captures what appears to be an angry reaction from protesters who witnessed the strike.

The same officer then removes an extendable baton from his left pocket and strikes the woman on her legs. The footage is not clear, but the woman appears to fall to the ground. The crowd again erupts angrily with chants of "shame on you".

The footage was shot by Tristan Woodwards, a 25-year-old administrator from Basingstoke, placed on YouTube and subsequently handed to the Guardian. Woodwards said last night he felt the officer had "abused his power".

"If someone was chucking a bottle or hitting a police officer I could have understood their behaviour," he said. "She [the woman] wasn't doing anything out of order. He's pretty tall and pretty big. Hitting a small woman isn't the most acceptable thing he could do."

The film is one of a number showing alleged police brutalities obtained by the Guardian since the footage showing Tomlinson being attacked by an officer.

Referring to the latest footage, a spokeswoman for the Independent Police Complaints Commission said: "The IPCC has been made aware that the Metropolitan police service will be referring an incident to us following footage which has come to light this afternoon. As soon as we get the referral, we will look into it and decide the best way to progress an investigation into the actions of the officer involved."