Metropolitan police officers fired a Taser nine times at a man sitting on a train in the belief he was carrying a weapon in his briefcase.

The use of Tasers on a train comes as the commissioner of the Met police, Bernard Hogan-Howe, faces questions over his suggestion that more of his officers should be armed with the weapons.

Hogan-Howe said this week he wanted to see more Tasers in response cars and Scotland Yard has confirmed work is going on to review the availability of Tasers for its officers.

Hogan-Howe was challenged about his statement about Tasers by members of the Metropolitan Police Authority on Thursday.

In an at times rowdy exchange, MPA member Cindy Butts urged caution saying: "We will see ourselves sleepwalking into a style of policing we have fought long and hard to move away from."

But Jennette Arnold said she supported the use of Tasers. "If a Taser had been used in the incident with Mark Duggan [who was shot dead by police in Tottenham, north London in August] that man would be alive today," she said.

Justice Livingstone said he was Tasered four times to the chest and when that did not affect him, officers Tasered him three times to the back of the head and twice to his hand, as he sat on a train in Norwood Junction in south-east London last week.

When he was finally detained police found a toy gun inside his briefcase. Livingstone told the Guardian he had bought it earlier that day as a present for his son.

Police were called to the station after an emergency call from rail staff that there was a man on the platform waving what appeared to be a gun.

British Transport police, supported by firearms officers from the Met, arrived at the station and boarded the train.

BTP said Tasers were used by Met officers to restrain the man when he failed to comply with officers' requests to remain seated. Scotland Yard said a Taser was fired several times after the suspect moved towards officers while shouting and refusing to move his hands from his pockets.

The Met police and British Transport Police said the suspect was in possession of an "imitation" firearm.

Livingstone, who said he had no history of mental health problems, had bought the toy gun earlier for his son's birthday. "It was 99p," he said.

The father of two said he had been sitting on the train when he first saw officers. "I was sitting near an elderly English man and I asked if I could read his FT. I was sitting reading the FT when these four officers rushed on to the carriage.

"Someone sitting by me raised his hands and said: 'I've done nothing wrong.' I saw everyone in the carriage leaving, and I picked up my briefcase and paper to get up to leave.

"The police shouted: 'Sit down.' So I sat down patiently. They said: 'Open your briefcase,' which I did. They saw the toy gun. Then a male police officer opened fire with a gun which jammed.

"So then they jumped at me and used the Taser four times at my chest. That did not have any effect, I felt no current. They then held me down, grabbed on to my head and pinned me down and shot me in the back of the head with the Taser three times and I felt the current.

"They tied my legs and took me off the train to the platform."

Scotland Yard denied any other firearm had been used.

Livingstone said he was taken to a police station in Victoria where he claims officers made fun of what he was wearing – a long trench coat and black hat. He was stripped naked, he said, and refused access to a lawyer.

He was eventually sent to Bethlem Royal hospital in Beckenham where he was sectioned under the Mental Health Act. But on Wednesday, after he made an appeal to the mental health tribunal, he was released and is now at his home in south London.

Scotland Yard said attempts to physically restrain the man had failed so a Taser was deployed.

The spokesman said the man was Tasered a number of times but this seemed to have no effect. Eventually, officers were able to physically restrain the man and he was removed from the train and into BTP custody, the Met said.

BTP said its officers were called along with the Met to reports that a man was on the platform waving a gun.

Livingstone said he would be making a formal complaint about his treatment.