The Guardian obtained this footage of Ian Tomlinson at a G20 protest in London, shortly before he died. It shows Tomlinson, who was not part of the demonstration, being assaulted from behind and pushed to the ground guardian.co.uk

An inquest opened today into the death of Ian Tomlinson, the 47-year-old newspaper seller who collapsed and died shortly after being assaulted by a police officer at the G20 protests.

Tomlinson's family called for the inquiry, which has been adjourned pending further investigations, to be "thorough and far-reaching".

An official at the City of London coroner's office said coroner Paul Matthews had decided to open the inquest "because of a combination of evidence, including that released by the media".

Tomlinson's family lawyer said in a statement: "The family are pleased that the coroner has today announced that there will be an inquest into Ian's death. They hope that it will be a thorough and far-reaching inquiry into all the circumstances leading up to his death.

"They are also waiting for the results of the second postmortem examination – which took place today – in which Dr Nathaniel Cary was jointly instructed by the family and the IPCC."

Earlier, a former senior police officer said that the policeman filmed assaulting Tomlinson should be suspended from duty and arrested.

Brian Paddick, a former Metropolitan police deputy assistant commissioner, said public confidence in the force could be damaged if it did not take "decisive action".

He warned that the Met could be open to accusations of double standards when dealing with officers suspected of wrongdoing.

The officer, who has not been named, was expected to be questioned today under criminal caution by the Independent Police Complaints Commission .

He identified himself to his manager and the IPCC yesterday as fresh pictures suggested he had removed his shoulder number and covered his face with a balaclava before hitting Tomlinson with a baton and then pushing him to the ground on Cornhill, in the City of London, last Wednesday.

"There is already ... concern among some people in the community that the police are not being held to account for their actions," Paddick told the Guardian. "If that had been a member of the public caught on video doing that, they would have immediately been arrested.

"The police are in danger of being accused of double standards by not suspending and arresting the officer.

"There is a danger of undermining public confidence in the police by not taking decisive action."

The officer in the video has not been arrested on suspicion of assault or suspended from duty by the Met, and the IPCC has not ordered the force to do so.

The Guardian handed the video showing the officer striking Tomlinson to the IPCC on Tuesday.

After intense publicity, the officer came forward, along with several other police officers shown in the video.

Other developments saw:

• The IPCC reverse its decision to allow City of London police officers to investigate the death.

• A second postmortem examination ordered as the IPCC confirmed that it would conduct a criminal investigation.

• Several top-level crisis meetings inside Scotland Yard.

• The Crown Prosecution Service liaising with the IPCC over possible charges.

• The emergence of Channel 4 footage, taken from another angle, which clearly shows the officer hitting Tomlinson with his baton before pushing him to the ground.

The officer involved could face a manslaughter charge if a link between the assault and Tomlinson's fatal heart attack minutes later is proved. "There is no excuse for what he did," a senior police source told the Guardian, adding that, at the very least, the officer had committed a serious disciplinary offence and a criminal assault.

Yesterday, Scotland Yard said four Met officers had come forward, including one who had told his team leader that he was potentially involved in the assault.

Tomlinson was on his way home at about 7.20pm when he was hit with a baton and pushed to the ground near the Bank of England.

Witnesses suggested the attack was the second time police had assaulted him.

At first, the City police investigating the death said Tomlinson had died of natural causes, but the video footage forced the IPCC to review its role in the inquiry yesterday.

Deborah Glass, a senior commissioner at the IPCC, said the watchdog was removing the investigation from City police and launching an independent inquiry.

"People are rightly concerned about this tragic death and this footage is clearly disturbing," she said.

The first postmortem on Tomlinson found he had died of a heart attack, but neither the police nor the IPCC would reveal whether any marks indicating an assault had been found on his body.

There had been intense pressure on the IPCC to use its powers to conduct an independent investigation after the Guardian footage was released.

Sir Paul Stephenson, the Met commissioner, said the images "raise obvious concerns" and his force fully supported an inquiry.

A source close to the IPCC said the issues for the investigation were: "Was an offence committed? Secondly, did it contribute to his later death? Would that incident have caused the heart attack?"

The home secretary, Jacqui Smith, said it was important that the IPCC inquiry was completed as soon as possible, adding: "If it identifies the need for a criminal investigation, then that also needs to be pursued."