The Metropolitan policeman who struck and pushed Ian Tomlinson as he walked away from riot officers on the fringe of the G20 protests in London has been sacked with immediate effect after a disciplinary hearing found he had committed gross misconduct.

It was "inconceivable" that Simon Harwood, who was cleared of Tomlinson's manslaughter in July following one of the most high-profile cases of police misconduct in recent years, could ever work as a police officer again, the three-strong panel ruled.

PC Simon Harwood. Photograph: Ben Stansall/AFP/Getty Images

Commander Julian Bennett, who chaired the panel, said: "PC Harwood's use of force in this case cannot be justified. His actions have discredited the police service and undermined public confidence in it.

"PC Harwood has accepted that it would be impossible for him to ever again serve as a police officer, whether within the MPS [Metropolitan police service] or any other police force – we agree, as we consider it inconceivable that he could ever perform a role in the police service again."

Harwood, whose long and at times murky prior disciplinary record was not disclosed at his trial, would be sacked with immediate effect, Bennett said. However, he will keep his pension entitlement as he has not been convicted of a crime.

Tomlinson, 47, died shortly after being shoved to the ground by a riot policeman later identified as Harwood. An inquest last year ruled that Harwood unlawfully killed him, but a trial jury acquitted the officer of manslaughter in July.

The disciplinary panel, sitting in public for the first time in the Met's history, was initially going to try to reconcile these contradictory verdicts by ruling on whether Harwood's actions contributed to Tomlinson's death, even inadvertently, but this element was removed after representations from the officer's lawyers, dismaying Tomlinson's widow and children.

A video still showing Harwood pushing Ian Tomlinson prior to his death. Photograph: Sarah Lee for the Guardian

Tomlinson's stepson, Paul King, described the process as "a whitewash" after walking out of the Met police administrative centre in Earls Court, west London, before the final ruling had been given.

He said: "It's like they have just let PC Harwood resign. The conflicting verdicts of the inquest and criminal court still need to be resolved. We haven't given up; we will now be looking to the civil courts for the final judgment on who killed our dad.

"Who killed Ian? We know," King added. "It's just a question of getting them to own up."

Addressing the panel earlier in the one-day hearing, Patrick Gibbs QC, representing Harwood, 45, said the officer had twice offered to resign from the force, firstly after the inquest and then after the trial.

"He thought that that was the right thing to do," Gibbs said. "He wanted to minimise further embarrassment to the Metropolitan police service." Both offers were refused, the lawyer added.

Gibbs added: "As far as the use of force, he completely accepts that the force he used was completely unnecessary."

However, Gibbs said, any decision on whether Harwood's actions killed Tomlinson would be "gratuitous and provocative, designed to provoke a retrial of Mr Harwood on charges on which he has already been acquitted".

Tomlinson died shortly after Harwood struck him on the leg with a baton and pushed him to the ground as he tried to make his way home past police lines following a day of protests connected to the G20 summit.

An initial postmortem examination said Tomlinson, who was a long-term alcoholic, died of natural causes.

But video footage, handed to the Guardian by a witness to the incident, revealed Harwood's actions, and two further postmortem examinations said the cause of death was internal bleeding caused by Tomlinson falling to the pavement after the push.

The jury at the manslaughter trial was not told details of Harwood's past record, notably that he quit the Met on health grounds in 2001 shortly before an earlier planned disciplinary hearing into claims that he illegally tried to arrest a driver after a road rage incident while off duty, altering his notes retrospectively to justify the actions.

Harwood was nonetheless able to join another force, Surrey, before returning to serve with the Met in 2005. He also allegedly punched, throttled, kneed or threatened other suspects while in uniform in other incidents. Most of the complaints were unproven.

It is only the second time the Independent Police Complaints Commission has instructed police to hold a disciplinary hearing in public following a law passed in 2008.

The only other public hearing concerned officers accused of failing in their duty when they did not respond to repeated calls from Colette Lynch, a young woman in Rugby, Warwickshire, about threats from her ex-partner. He stabbed her to death days later.