A policeman accused of assaulting a Brighton G20 protester with a metal baton was described as an "extremely good officer" by his boss today.

Metropolitan Police Sergeant Delroy Smellie, 47, is on trial charged with beating animal rights activist Nicola Fisher.

City of Westminster Magistrates' Court heard evidence from his manager Inspector Derek Renton, who has known him for 15 years.

The senior officer said he head-hunted Smellie to his part of the force's territorial support group because of his abilities.

He said: "He was a capable supervisor and very mature and confident in his own abilities and an extremely good officer. I knew he would be an asset to my team.

"He is a very level-headed officer. He just does not do panic. He thinks things through very carefully. That is the same not just in public order, but in any facet of his policing ability."

Asked by Smellie's barrister Lisa Wilding if he would ever lose self-control and lash out, Mr Renton replied: "No."

The senior officer went on to describe how Smellie once talked a violent mentally ill man out of a lengthy stand-off at a London hospital.

He added: "The officer did really well in that situation because he was able to defuse quite a volatile situation."

The court has heard how Smellie shouted at, pushed and hit Ms Fisher with the back of his hand as tensions rose outside the Bank of England on April 2 last year.

The prosecution allege he then went beyond his legal powers by striking the 36-year-old twice across the leg with an extendable metal baton.

The clash was caught by several photographers and on video, gaining international notoriety when one version was posted on the website YouTube.

Mr Renton said he was present outside the Bank of England during the vigil to mark the death of Ian Tomlinson the previous day, but did not see the incident.

He described how officers grabbed a few hours' sleep on mattresses at their base and some did not get any rest at all after a long day policing protests on April 1.

Earlier, Inspector Greg Gilbert, of City of London Police, said tactics to contain suspected troublemakers outside the Bank of England went wrong.

He said insufficient back-up arrived to relieve a cordon of his officers, leaving police facing a vocal group who could not move while other protesters moved freely behind them.

Mr Gilbert said there were reports of missiles being thrown from the crowd and there were people among them who were wanted over an attack on a bank the previous day.

The court heard Smellie made a note of the clash in his pocketbook in which he said his actions were justified under "common law to defend colleagues".

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

The case continues.