A police officer accused of fatally injuring an unemployed man during protests in central London claimed that the victim was “almost inviting physical confrontation” before he was struck with a baton and shoved to the ground, a court heard today.

Pc Simon Harwood took the witness stand for the first time today and told a jury that he believed that the unemployed alcoholic was being deliberately obstructive and tacitly encouraged police to move him during violent demonstrations three years ago.

The officer, 45, said that he struck Ian Tomlinson across the thigh with a baton to encourage him to move away from police lines as he ambled away with his hands in his pockets. In a statement to the police watchdog in 2009, he said that someone with their hands in their pockets represented at least “an unknown risk”.

“From where I saw him from, he looked like he wasn’t going to move and was looking at police as if he wanted them to move him away,” he told Southwark Crown Court today.

“At the time I thought he was obstructing it (the police line) not allowing us to achieve our objective… I believe he was doing it on purpose.”

Mr Tomlinson was caught up in the violent protests on the eve of a meeting of G20 leaders as he tried to make his way home across London after a day’s drinking with friends. The court has heard that he was struck by Pc Harwood just after the officer had been publicly humiliated by the failure to arrest a protester scrawling an obscenity on a police van.

Pc Harwood said today that he became isolated from other officers during the protest on April 1, 2009 after trying to arrest the young graffiti writer who wriggled free from the policeman’s grasp after shrugging off his coat.

He said the increasingly agitated crowds were shouting at him and his sole aim was to “get the hell out of there, basically”.

“It was as if everyone was out to get me for what I had done in trying to get the graffiti man,” he said.

Pc Harwood, the driver of police carrier and described as an “experienced” officer, left his vehicle and joined other officers for his own safety, he told the court, before he encountered Mr Tomlinson. He said that he had not expected him to fall over when he pushed him.

Pc Harwood said that he last saw Mr Tomlinson walking from the scene. The 47-year-old walked about 75 yards before he collapsed and later died less than an hour later.

The officer said he thought little of what had happened in the immediate aftermath of the “momentary” incident. His involvement only became clear after footage of the incident was repeatedly shown on television days later, the court heard.

Inspector Timothy Williams, the head of a specialist public order team based in Catford, told the court that the footage was screened at the moment that Pc Harwood came into the station to speak with him.

“He watched it and he said to me that he thought he was the officer concerned,” Inspector Williams said. “He had his head in his hands facing towards the ground and was sort of looking up at me and obviously he looked shocked.”

The court heard that Pc Harwood made three statements to the police watchdog during meetings in the months after the death but declined to answer any questions.

In one statement, he said that Mr Tomlinson was “almost inviting physical confrontation and being moved on”, the court heard.

Pc Harwood, of Carshalton, Surrey, denies manslaughter. He said that his use of force was necessary and proportionate.