A British police officer has been found guilty of gross misconduct and fired from the London force over an incident that resulted in the death of a man during a G20 summit in London in 2009.

Officer Simon Harwood hit 47-year-old newspaper vendor Ian Tomlinson with a baton and shoved him to the ground as Tomlinson tried to find his way out of a cordon put up to contain the protesters.

Tomlinson collapsed and died moments later. His death became a rallying point for those who alleged that police had brutalised the demonstrators.

Harwood was tried and acquitted of manslaughter in July, but on Monday a police disciplinary panel ruled that his actions amounted to gross misconduct.

“PC Harwood’s use of force in this case cannot be justified,” said Commander Julian Bennett, who chaired a panel made up of two police officers and a civilian. “His actions have discredited the police service and undermined public confidence in it.”

Defence lawyer Patrick Gibbs said Harwood accepted the ruling.

The panel declined to consider whether Harwood’s actions had contributed to Tomlinson’s death, even though a coroner’s inquest ruled last year that the newspaper seller had been “unlawfully killed”.

That angered Tomlinson’s family. His widow and two stepsons walked out of the room saying “Whitewash” as the hearing ended.

The family’s lawyer, Jules Carey, said the family planned to take action in the civil courts.

“They want it to be determined finally whether or not PC Harwood is guilty as an employee of the police of killing Ian Tomlinson,” he said.