Senior police and press officers are under investigation after complaints they deliberately misled the public over the death of Ian Tomlinson during the G20 protests.

In a move that escalated the controversy around police involvement in Tomlinson's death last month, the Independent Police Complaints Commission announced today it had launched a new inquiry into "media handling" by the Metropolitan police and City of London police.

The announcement followed a complaint by Tomlinson's family last week about information released by police about his death. The investigation could result in disciplinary action for misconduct or criminal charges.

"Not only the Tomlinson family, but also many members of the public and MPs, have raised with us concerns about whether the police either misinformed the public about the circumstances of Mr Tomlinson's death or failed to correct misinformation about how he died," said IPCC deputy chair Deborah Glass.

"I have therefore decided that not only will we investigate the family's specific complaint about the content and timing of the [Met's] media communications on the night of 1 April, but that we should also seek to determine, as far as practicable, the state of knowledge that both the Metropolitan and City of London police had about any police contact with Ian Tomlinson between 1 April and 7 April 2009."

Sources with detailed knowledge of the investigation said the IPCC is also questioning whether City of London police may have deliberately withheld crucial information from the watchdog.

The IPCC was first told of potential contact between police and Tomlinson on 3 April, 48 hours after the death. However, the Guardian has seen a confidential police document which suggests City of London police knew about potentially violent contact with Tomlinson the previous day. The City of London police memo, marked "Restricted Investigation" and written at 5.02pm on 2 April, acknowledged the existence of a "series of photos" of Tomlinson.

The memo was referring to four images, all of which showed Tomlinson at the feet of riot officers at the Royal Exchange, where it later emerged he was struck with a baton and pushed to the floor. The IPCC will now consider a series of statements and briefings by police in the days after Tomlinson died near the Bank of England on 1 April at around 7.30pm.

Four hours later, at 11.36pm, the Met released a statement announcing the death, which included the claim that officers giving Tomlinson treatment were impeded by protesters throwing missiles, believed to be bottles.

The Met's allegation was strongly denied by several protesters who went to Tomlinson's aid and called an ambulance. Later, the Met said it had not "deliberately misled" the media about the death.

Concerns have also been raised about informal guidance given to journalists, who were briefed by police that Tomlinson's family were "not surprised" he had died. The family deny having said that.

City of London police will be investigated over a statement released about the first postmortem into Tomlinson's death, which said he "suffered a sudden heart attack while on his way home from work", but did not mention that the pathologist had found injuries to his body and a substantial amount of blood in his stomach.

Around the same time, a City of London police officer is understood to have told members of the Tomlinson family that Tomlinson's arteries were clogged and the death was an accident waiting to happen, but made no mention of other injuries.

A second postmortem concluded Tomlinson died of internal bleeding.

The Met officer shown in the footage attacking Tomlinson, who has been suspended and questioned on suspicion of manslaughter, has not released the details of a third postmortem conducted on his request. Yesterday, the officer's lawyer would not comment on speculation that the third postmortem, like the second, indicated that bleeding in Tomlinson's abdomen led to his death.