A Lewisham police officer is facing jail after smashing a student's tooth out during the tuition fee protests and telling him "not me mate, you slipped on the metal fence".

PC Andrew Ott, 36, from Rochester, Kent, was taped threatening to "batter" protesters on his own standard-issue dictaphone and saying he wanted to “poke that little c*** right in the eye”.

Student William Horner lost part of his front tooth as he was restrained by Ott after escaping a "kettled" area during the demo in Parliament Square on December 9 2010.

Ott was convicted of assault occasioning actual bodily harm but cleared of falsifying an account of the incident with colleagues by a jury at Southwark Crown Court.

The jury acquitted him and Bexley police officers PC Calvin Lindsay, from Leytonstone, east London, and PC Thomas Barnes, from Greenhithe, both 31, of perverting the course of justice.

Judge Jeffrey Pegden QC warned Ott that a custodial sentence "would be at the forefront of the court's mind".

The tuition fees protest had kicked off in the morning and lasted all day with episodes of violence and one officer being knocked off his horse by thrown missiles, jurors heard.

Police officers were deployed in large numbers in full riot gear to combat the "frightening" protests that saw statues in Parliament Square daubed with graffiti and concrete blocks hurled through the air.

Second year university student Mr Horner travelled to the protests on a coach from Royal Holloway University in Surrey.

The politics and international relations student said he went to the march to "exercise my opinion on rising tuition fees".

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He told jurors the protests were "peaceful" on the march from Bloomsbury to Westminster but grew violent when they entered the cordoned-off area.

He said "There had been some fences in place and when the protest march reached Parliament Square I think some people pushed over some of those fences and pretty much straight away the entire crowd of protestors surged into Parliament Square and that is where we stayed for the next few hours.

"There were some incidents of violence and it increased in intensity the longer people remained there.

"I remember some people destroying some windows in the Supreme Court."

But he denied being involved in any violence himself and said he was trapped in the "kettled" area with no means of escape, toilets or water for hours.

He said: "I made no plan to leave by forcing my way or climbing over a fence and getting out the way I did, I did so merely as a moment occurred when I thought I could."

He spotted a police line that was "sparse" with offices standing up to four metres apart and seized the opportunity to try to escape to Waterloo and get home, jurors were told.

He said: "I climbed over the fence and then as soon as I was on the other side I was spotted by a police officer and shouts were made towards me or in regards to me - shouting at officers to stop me.

"I then ran in the direction I had intended to leave, I ran between St Magaret's Church and Westminster Abbey.

"There was at this point a number of officers chasing me, I knew so because I could hear them shouting.

"I don't believe they shouted at me to stop but I recall the officers shouting 'stop him!'”

Mr Horner ran into a corner but soon realised he was trapped and turned around with his hands in the "surrender" position to see Ott sprinting towards him.

He said: "He raised a circular riot shield and he hit me into the front of my face with the shield with some force.

"Instantly the blow broke my front right tooth pretty much in half.

"It knocked me over and within seconds PC Ott was on top of me, pinning me down and applying handcuffs to me."

He added: "Initially what had happened, I could feel part of my tooth was missing with my tongue, I could taste a bit of blood.

"Instantly I believed PC Ott had acted unprofessionally, he used force which wasn't justified."

Mr Horner demanded Ott hand over his personal identification number, but the officer had to be asked three times and appeared "reluctant", the court heard.

Mr Horner said: "He stood up and he left in the direction he had come from and I didn't see him again."

Giving evidence Ott said: "I believed he had done something or was about to do something, I wanted to contain him.

"I had full knowledge of what I could and couldn't do and I wasn't about to start attacking him like everyone says.

"I bring my shield around, I believe it was on my left arm, and the momentum and also the fact that I bring my shield around my body, I collided with him."

Ott said he was using the riot shield to "create distance".

He said: "I struck him with the shield at that point, at that moment in time my threat assessment was high.

"He was a threat to me, I dealt with it as I saw fit.

"Hindsight is fantastic, would have I have done something different? Absolutely, I wouldn't be here but I did what I did.

"I struck his upper body, if his head got hit then it got hit I didn't aim for his head.

"To get a chipped tooth from a shield like that - unlucky."

No further action was taken against Mr Horner.

Recordings taped on Ott's equipment revealed the cop saying: "Boys if you get a clout off that f*****g geezer there... you have a go, he has been a f*****g nightmare."

Ott was also heard saying he was going to "poke that little c*** right in the eye".

When asked "did you poke him in the eye?" by Judge Pegden, Ott replied: "Yes, probably by accident sir.”

He could also be heard boasting he was "more covert" because he wasn't wearing his bright jacket and his identification number was "not well known".

Public servant Rosalind Leaming was making her way to collect some papers from the Houses of Parliament at about 8pm when she witnessed the attack.

She said: "I saw a boy, and I say a boy because he looked young, and he came running to where we were and there was a gate in between us and he put his hands on the gate and he was trying to open the gate.

"It was clear that the gate was shut and he was trying to get through the gate but he was unable to do so, he was at a dead end."

She added: "He was young and he just looked frightened, and when he was on the ground his face just looked squashed, I don't know if there was an expression on it.

"I didn't hear him speak at all throughout the whole thing."

A sentencing date for Ott has yet to be set.