PC Simon Harwood had been expected to remain beside three police vans but had become separated, inquest hears

The police officer accused of attacking Ian Tomlinson moments before he died at the G20 protests was a van driver who had strayed from his post without the knowledge of his supervisor, an inquest has heard.

PC Simon Harwood had been expected to remain stationed beside three territorial support group (TSG) vans parked near the Bank of England, on the evening of 1 April 2009.

The inquest, which has so far focused on the minutes leading up to the attack, heard how Harwood became separated from the other van drivers when he tried to arrest a protester whom he suspected of spraying paint on a van.

The jury had previously been shown footage of Harwood grabbing a male protester and dragging him into the crowd.

Separated from his unit, and apparently isolated, he then struck out at least one other protester and appeared to drag a press cameraman to the ground.

Moments later, at about 7.20pm, Harwood came across Tomlinson, struck him with a baton and pushed him to the ground. Tomlinson, a 47-year-old father of nine, collapsed and died minutes later.

Harwood's supervising officer, TSG sergeant Emma Shaw, said she had appointed him to be a van driver for the protests. She said he missed one of two briefings from senior officers before the protest, when constables were told to be "firm but fair" with protesters and display their badge numbers at all times.

Harwood was filmed with his face covered with a balaclava on the evening of 1 April and his shoulder numbers were not visible. Shaw told the jury there had been problems with shoulder numbers falling off uniforms.

She said that van drivers were normally expected to remain by their vehicles, and she did not anticipate Harwood would stray from his post when he she left him at the van, at about 6.15pm.

However, when Shaw returned to the vehicle three hours later, Harwood told her that he had been separated from the other officers after trying to arrest a suspect who had sprayed paint on a colleague's van.

"He said that one of the carriers had been damaged and that he tried to arrest the man suspected for it, and got separated from the carrier," Shaw said. "He ended up with another police serial for a short time and returned. I asked if was okay and he said that he was, and I noticed there was some blue writing on the van."

But Harwood failed to tell his sergeant about the incident in which he struck Tomlinson. Asked if he made her aware of the incident with Tomlinson at any point that night, including when they had returned to base in south-east London, Shaw replied: "Not that night, no."

Under questioning from the deputy assistant coroner, Judge Peter Thornton, Shaw agreed that officers in a public order officers would not necessarily arrest a suspect for a petty offence, if it was likely to incite further problems.

Earlier, the jury heard from witnesses who saw Tomlinson in nearby Lombard Street, about 20 minutes before he was struck by Harwood. He was said to have appeared drunk and disoriented, and at one stage had to be moved out of the road to make way for a passing police van. "He was open-mouthed," said James Stone, a City worker attending a gym in the street, in a statement read out to court. "He had a vacant expression everywhere he looked."

"His responses were slow," said Warren Fraser, an IT worker. "He looked as if he was in his own world."