A G20 protester allegedly assaulted by a police officer was described as acting "erratically" and like a "lunatic" by two eyewitnesses today.

Two office workers looked on as animal rights activist Nicola Fisher joined dozens of demonstrators outside the Bank of England on April 2 last year.

The office workers told City of Westminster Magistrates' Court how they watched a confrontation between her and Metropolitan Police Sergeant Delroy Smellie.

Mark Ellul, who works in an office in Cornhill, said his eyes were drawn to Ms Fisher as she was "hyperactive" and behaving "erratically" in the moments before the clash.

Giving evidence for the prosecution, he said: "I think I described her at the time as a cat on a hot tin roof."

His colleague Tracey McDonnell said Ms Fisher was "playing up to the cameras", acting aggressively towards police and throwing orange juice at Smellie.

She said: "There were a lot of people there but we were drawn to her as she was bouncing around and the most aggressive person there at the time."

Smellie, a member of the Met's territorial support group, is on trial accused of assaulting the 36-year-old, from Brighton, during a vigil to mark the death of Ian Tomlinson.

The court has heard he lawfully pushed Ms Fisher and hit her with the back of his hand, but prosecutors claim he committed a crime by striking her twice with a metal baton.

The clash was caught by several cameramen and photographers, gaining international notoriety after a recording of it was posted on YouTube.

Mr Ellul and Miss McDonnell said they contacted the Independent Police Complaints Commission (IPCC) after watching media coverage of the incident. Both said they felt the coverage gave an unfair and inaccurate portrayal of the officer's actions.

Mr Ellul said: "Nicola Fisher charged at the officer. She was being very aggressive towards the officer. She was right up in his face and appeared to shout and be confrontational.

"At that time there was a group of people who were kind of surrounding the officer. He was kind of on his own. There were officers with their backs to him.

"Nicola Fisher was being very aggressive and confrontational towards the officers, everyone was getting closer and closer and then he raised his hand and slapped her around the face."

Mr Ellul added that he felt Smellie was vulnerable because he was caught behind a line of officers who were looking in the other direction.

Miss McDonnell said the group of protesters had been "antagonised" by the arrival of a large convoy of specialist police vans carrying public order officers.

She said: "She was, I hate to say it, aggressive towards him. She kept coming at him. There was pushing between them. She was pushing him, definitely, being physical.

"She was holding a carton in her hand. It looked like orange juice to me and it looked like she was throwing it at him."

The court heard Miss McDonnell described Ms Fisher as behaving like a "lunatic" and being "out of control" in a statement she gave to the IPCC.

Smellie, 47, who gave his address as care of a police territorial support group base in Larkhall Lane, Clapham, denies one charge of assault by beating.

The case, due to end on Thursday, will continue tomorrow when the defence is expected to begin.