It began with an anodyne press release from the Metropolitan police more than three hours after Ian Tomlinson died. It ended with a police officer and an investigator from the Independent Police Complaints Commission asking the Guardian to remove a video from its website showing an unprovoked police assault on Mr Tomlinson minutes before his heart attack.

In the space of five days through a combination of official guidance, strong suggestion and press releases, those responsible for examining the circumstances surrounding Mr Tomlinson's death within the City of London police and the IPCC, appeared to be steering the story to what they thought would be its conclusion: that the newspaper vendor suffered an unprovoked heart attack as he made his way home on the night of the G20 protests.

Late last Friday, after investigators from the IPCC had spoken to detectives from City police, the commission which claims it is the most powerful civilian oversight body in the world, was preparing to say it did not need to launch an inquiry into the deathduring one of the most controversial recent policing operations.

But the release of the video by the Guardian this week, which revealed Mr Tomlinson was subjected to an unprovoked attack by a Met riot squad officer minutes before he died, has forced the IPCC to step up to the demand that it launch a full independent inquiry.

"They have caught a real cold on this," said a senior source. "They were very slow, they clearly didn't think anything was wrong and they didn't look for it. Sometimes they just don't seem to be very independent."

A former IPCC insider went further, blaming a "cosy" relationship with the police for the commission's failure to act quickly. "The problem with the IPCC is that it is too late to start inquiries and they go on for too long," said John Crawley, a commissioner for four years. "They should have picked this up as an independent investigation straight away. There was strong public interest given the concern about the 'kettling' tactics being used to police the protests and the need to gain the confidence of those demonstrators with information to come forward to someone who wasn't the police."

Policing operation

Until yesterday it all seemed to have gone so well for Met commanders. For several hours on 1 April thousands of demonstrators had been trapped in a cordon outside the Bank of England and troublemakers were identified on handheld cameras carried by police teams.

Around midnight teams of baton-wielding riot police with dogs were sent to clear hundreds of peaceful protesters from the climate camp in Bishopsgate while the national media was absent.

Dissenters, who claimed officers were pumped-up, were dismissed by senior figures who said their teams were involved in a difficult balancing act of respecting the right to protest while tackling about 300 people committed to violence and criminal damage.

When Mr Tomlinson died during the police operation, the Met chose to delay announcing it for more than three hours. Its statement pointed a finger at protesters. "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," it said. "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.

The force refused yesterday to reveal why it took so long to announce someone had died within the demonstration area, or to address the question of where the information about missiles being thrown at police officers had come from. Witnesses who aided Mr Tomlinson have always contested that police had been attacked by a hail of missiles.

Thus began the official narrative of Mr Tomlinson's death. The next day the IPCC said the incident had been referred to it by the Met and it would be "assessing the circumstances throughout the day ... examining CCTV and attending the postmortem". In the meantime the investigation was being handled by the City of London police because it happened in its area. At Gold command headquarters, where senior officers were gathered on Thursday there was talk of the Tomlinson family mentioning concerns to police about his health. That line was seized upon and used as heavy guidance for journalists who spoke to City police about the death in the days that followed.

"His family were not surprised to hear what had happened," the guidance went. When pressed about the nature of the inquiry and whether Mr Tomlinson had any contact with officers, journalists were told speculation "upset the family".

Photographs

Requests to speak to the family were met with a refusal and instead City police put out a statement, in which the family were quoted as saying: "The police are keeping us informed of any developments."

But one major development was kept from them. On Friday, the Guardian made City of London police aware it had obtained photographs of Mr Tomlinson on the pavement in front of riot officers. It has since emerged that those images showed the immediate aftermath of the attack. While police did not see the images, they were aware of a suggestion Mr Tomlinson had been involved in an altercation with a police. The family were not told this.

Throughout that day the police refused to talk about why Mr Tomlinson's postmortem examination had been twice delayed. The IPCC said it was still assessing what was going on and could not comment on reports of altercations.

In reality, Crawley said, the IPCC's assessment would have involved an investigator talking to City police and viewing some CCTV footage. What the commission did not do was seek or speak to civilian witnesses, or investigate other sources of information before making its decision.

On Saturday details of Mr Tomlinson's postmortem examination were released by City police. Independent approaches to the coroner were met with a refusal to comment. City police would not comment on whether any other findings had come from the postmortem, for example marks on his head and body from a baton blow.

On Sunday, the pictures obtained by the Guardian showing Mr Tomlinson on the ground in front of police were published.

Around 10.30 am the Tomlinson family attended the scene of the death, where they spoke to the Guardian about allegations he had been assaulted by police. They said they were glad the pictures had come out and wanted more answers. They were concerned about allegations that Tomlinson had been assaulted. They gave the Guardian their names, telephone numbers and address and then attended a church memorial service.

It was then, during the service, that the family's police liaison officer told the Guardian he was extremely unhappy the paper had spoken to them. He told the Guardian's reporter not to contact the family "for 48 hours".

Meanwhile official guidance from the IPCC to another Guardian journalist accused the paper of doorstepping the family at a time of grief. The IPCC guided that the family had been deeply distressed by the newspaper's approach. On the same day the IPCC told journalists from rival publications there was "nothing in the story" that Mr Tomlinson had been assaulted by an officer. On Tuesday night when the video of the assault was released, an IPCC investigator and a City of London officer visited the Guardian's offices in King's Cross to be handed a dossier of evidence. They asked that the video was removed from the website, claiming it was "jeopardising" their inquiry and not helpful to the family. By now Tomlinson's family had found their own voice. They told the Guardian: "Now we do know police did have contact with him. Thanks for everything you have done so far."