Why did it take six days and citizen journalism to shed light on Ian Tomlinson's death? Nick Davies examines the role of the Independent Police Complaints Commission and asks who the media can trust

The family of Ian Tomlinson, who died at the G20 protest this month, are planning to file a new complaint to the Independent Police Complaints Commission (IPCC). This will deal not with the events that led to his death but with the fog of media misinformation that followed it. It is a complaint that will go to the heart of the way in which the news media operate - to the frequently undeclared relationship between reporters and the press officers on whom they rely and, in turn, the officials on whom these spokesmen rely on for much of their raw material. And it will pose a question that both sides often prefer to ignore: can they trust each other?

There were six days of substantially false coverage about a man who apparently died of a heart attack as he walked home while a screaming mob of anarchists hurled missiles at the police officers who tried to help him. Any inquiry into this media misinformation will want to find out whether that was simply the hyperbole of ignorant reporters or the product of bad practice at the Metropolitan police, the City of London police or the IPCC.

It was the intervention of ordinary people with cameras who provided their own surveillance of the protest that first led to questions about that version of the truth. An investigation by the Guardian suggests that an inquiry may find evidence of officials giving an incomplete picture.

At 7.30pm on Wednesday 1 April, as Mr Tomlinson lay dying on the pavement near the Royal Exchange in the City of London, Sir Paul Stephenson, the commissioner of the Metropolitan police, was several miles away at a party at Peelers restaurant, on the fifth floor of New Scotland Yard, to mark the retirement of the assistant commissioner Alf Hitchcock.

According to one guest: "He kept going out into the corridor, on his mobile. He looked very unhappy, stressed."

Four hours later, at 11.36pm, Scotland Yard issued a press release (see below), that, we now know, was seriously misleading - not because it included a direct falsehood, but because it failed to include the most important part of the truth, that Mr Tomlinson died after apparently being struck and pushed to the ground by a police officer. This press release was the result of some intense argument in the Yard's press bureau, with an earlier draft having been rejected.

The final draft, we have established, was approved over the phone by a regional director at the IPCC. Both Scotland Yard and the IPCC say that the press release was the truth as they knew it that night, that nobody who was involved in producing it knew, or had reason to suspect, that Mr Tomlinson had had any contact with a police officer.

A key task for any inquiry will be to find out why, if that were so, Scotland Yard that night referred the incident to the IPCC at all. That was an unusual move, certainly not one that occurs whenever a man has a heart attack in the street and/or when police officers try to save a man's life.

The IPCC's statutory guidance, however, requires police to refer to them "incidents where persons have died or been seriously injured following some form of direct or indirect contact with the police and there is reason to believe that the contact may have caused or contributed to the death or serious injury". However, both the IPCC and Scotland Yard say there had been no allegation of contact at the time: "It was treated as an unexplained death within the area of a policing operation that would need to be properly investigated and, therefore, the IPCC were informed as is routine practice in these circumstances."

Yet senior figures at Scotland Yard last week insisted, on the condition of anonymity, that the apparent assault on Mr Tomlinson had been detected by the police control room at Cobalt Street, south London, as soon as it happened and also that it had been "phoned in" by a chief inspector on the ground. A spokesman for the Metropolitan police denied this and said that, in response to the Guardian's inquiry, they had checked with every chief inspector in the operation, none of whom said they had called in such a report. On Thursday morning, under IPCC direction, the City of London police began an inquiry into the death. They also began to brief reporters with a line that appears to have surfaced first on the day after Mr Tomlinson's death at a meeting of the Gold Command group of senior officers who had policed the G20 protest. They heard reports from officers who had visited Mr Tomlinson's family that he had been in a poor state of health.

Without waiting for a postmortem to check this, City of London police briefed reporters. "On the Thursday, their line was that the family were not surprised by the death," according to one, "and that we should stop probing because the family didn't want this. He had health problems. 'There's a history there,' they were saying."

We now know that on the following day, Friday 3 April, this idea was substantially challenged from three directions: independent witnesses told the IPCC that police had clashed with Mr Tomlinson before his death; the Guardian warned the IPCC that it had photographs of Mr Tomlinson on the pavement at the feet of riot officers, apparently remonstrating with them; and, late that night, the preliminary report of a postmortem found that Mr Tomlinson had probably died of coronary heart disease but also found a number of injuries and a substantial amount of blood in his abdomen.

On Saturday, City of London police released an account of the pathologist's report, which highlighted the heart attack, but not the injuries or the blood in Mr Tomlinson's abdomen. This reinforced the existing police narrative, with Sunday papers recycling the line that he had died of natural causes. A second postmortem has since suggested that he died as a result of an abdominal haemorrhage. The City of London police press office say that everything it gave journalists was based on the information available at the time.

That Sunday, a senior IPCC official called the Guardian to complain that a reporter had been "doorstepping" the church where the Tomlinson family had gone to mourn the dead man. This was based on information given to the IPCC by the City of London police and accepted on good faith but, on investigation, turned out to be wrong.

Two days later, on the evening of Tuesday 7 April, the Guardian posted on its website the crucial video of Mr Tomlinson being pushed to the ground, and agreed to hand over to the IPCC a copy of the video as well as printed statements from witnesses found by the newspaper.

However, when an IPCC investigator came to the Guardian, with a City of London police exhibits officer, he asked for the video to be removed from the website on the grounds that it could prejudice the police inquiry and would upset the family. The deputy editor-in-chief who met him declined and pointed out that the Tomlinson family at that moment were in another part of the building, talking to Paul Lewis, the reporter who had driven the story, and publicly thanking the paper for its help.

The IPCC was involved in a similar, but tougher, manoeuvre last week when its lawyers attempted to get an injunction to prevent Channel 4 News from using a new video of the incident. A judge refused to grant it. The IPCC last week claimed that there was a particular passage in the footage that caused them concern but declined to identify it.

The IPCC has some history of publishing misleading press releases, often apparently reflecting the police account of an incident.

In the case of a man who died in police custody in Essex in 2005, the IPCC published two press releases containing inaccuracies, which led lawyers to write to them warning that the dead man's family "can be forgiven for coming to the conclusion that those who may have something to fear from the truth are seeking to 'spin' it for public consumption in an exercise in which the IPCC is appearing to play a part". After lengthy correspondence, the IPCC published corrections to both press releases.

In another recent case, the IPCC was forced to scrap a draft press release about a man who had been shot dead by police after the family's solicitor threatened to go to court to challenge its contents as prejudicial.

The solicitor, Tony Murphy of Bhatt Murphy, said: "These reports not only risk prejudicing inquest juries, they also signal a lack of balance and a failure by the IPCC to treat the police account with a healthy degree of scepticism. The IPCC is quick to examine potential motives of the deceased but much slower to probe the police line. This is detrimental to the IPCC's independence and credibility."

The IPCC told us they have no plans to investigate media handling of the incident, whether by themselves or others, but would consider any complaint they received.

The Scotland Yard press release

A member of the public went to a police officer to say that there was a man who had collapsed round the corner. That officer sent two police medics through the cordon line and into St Michael's Alley where they found a man who had stopped breathing. They called for support at about 19.30. The officers gave him an initial check and cleared his airway before moving him back behind the cordon line to a clear area outside the Royal Exchange Building where they gave him CPR.

The officers took the decision to move him as during this time a number of missiles - believed to be bottles - were being thrown at them. LAS [the London Ambulance Service] took the man to hospital where he was pronounced dead.

The Directorate of Professional Standards at both the MPS and City of London Police have been informed. The IPCC has been informed.