Video footage showing Ian Tomlinson being struck by a police officer guardian.co.uk

The police officer caught on video during last year's G20 protests striking a man who later died will not face criminal charges, the Crown Prosecution Service announced today.

Keir Starmer, the director of public prosecutions, said there was "no realistic prospect" of a conviction, because of a conflict between the postmortem examinations carried out after the death of Ian Tomlinson last year.

The newspaper seller died following the demonstrations on 1 April 2009 in central London. The official account that he died from a heart attack was undermined when the Guardian obtained video footage showing a riot officer striking the 47-year-old with a baton and shoving him to the ground shortly before he collapsed and died.

In a written statement the CPS admitted that there was sufficient evidence to bring a charge of assault against the officer, but claimed a host of technical reasons meant he could not be charged.

Tomlinson's stepson Paul King, flanked by his mother, Julia, said: "It's been a huge cover-up and they're incompetent."

King said: "He [Starmer] has just admitted on TV that a copper assaulted our dad. But he hasn't done anything. He's the man in charge ... why hasn't he charged him?

"They knew that if they dragged this out long enough, they would avoid charges. They knew just what they were doing. They've pulled us through a hedge backwards – now we have to go on living our lives."

The family solicitor, Jules Carey, said the decision was a disgrace and Tomlinson's relatives would be considering whether they could mount an appeal.

"Clearly it is a disgraceful decision," he said. "We now need to find out if there has been a lack of will or incompetence, and frankly there needs to be an inquiry into that."

The family, who went to the headquarters of the CPS in London to be told of the decision, had wanted a charge of manslaughter to be brought against the officer, who was named in media reports as PC Simon Harwood.

CPS decision

In a detailed letter setting out its reasons, the CPS said that the actions of the officer – seen striking Tomlinson with a baton then shoving him to the ground in the footage – were grounds for bringing a charge of assault.

It said: "The CPS concluded that there is sufficient evidence to provide a reasonable prospect of proving that the actions of PC 'A' in striking Mr Tomlinson with his baton and then pushing him over constituted an assault. At the time of those acts Mr Tomlinson did not pose a threat … There is sufficient evidence to provide a realistic prospect of proving that his actions were disproportionate and unjustified."

But the CPS went on to explain the obstacles to a prosecution posed by the subsequent postmortems.

The first police account, that he died from a heart attack, was confirmed by a pathologist, Freddy Patel, in the initial postmortem.

But a second postmortem, conducted by Dr Nat Carey on behalf of the Independent Police Complaints Commission (IPCC), found Tomlinson had died from internal bleeding.

Today the CPS said it could not bring a manslaughter charge because the conflicting medical evidence meant prosecutors "would simply not be able to prove beyond reasonable doubt that there was a causal link between Mr Tomlinson's death and the alleged assault on him".

It said it could not bring a charge for criminal assault because too much time had elapsed; a charge must be brought within six months. The CPS also ruled out bringing charges of actual bodily harm and misconduct in public office.

Tomlinson had his hands in his pockets and his back to the officer when he was hit. The video footage suggests that no other police officer went to his aid and it was left to a bystander to lift him to his feet. He appeared to stumble about 100 metres down Cornhill, clutching his side, before collapsing a second time.

Police initially led Tomlinson's wife and nine children to believe he died of a heart attack after being caught up in the demonstration. In statements to the press, police claimed attempts by officers to save his life by resuscitation had been impeded by protesters.

The IPCC said it would now pass its file to the Met, which will consider whether the officer should be disciplined. An inquest will examine the circumstances of Tomlinson's death and the case could be reconsidered by prosecutors after it is concluded.

A Metropolitan police spokesman said the force offered its "sincere regret" over the death of Tomlinson. He said the officer could still face misconduct proceedings once the force receives the IPCC report.

The CPS announcement comes five years to the day since another landmark incident involving police use of force. On 22 July 2005, officers shot dead Jean Charles de Menezes after mistaking him for a terrorist who was about to detonate a bomb. Then, the family of the innocent Brazilian criticised the CPS for failing to bring criminal charges against any individual.

The investigations

The Tomlinson family have criticised the time it took the CPS to reach its decision.

The first investigation was conducted by the IPCC. Its officials are understood to have reached a clear view as to whether enough evidence existed to support criminal charges.

They were able to complete their inquiries in just four months and submitted a file to the CPS by August.

Key to the investigation were hundreds of hours of footage and thousands of images shot by bystanders at the protest, which enabled them to piece together Tomlinson's last 30 minutes alive.

CPS officials had assured the family they would decide on whether to prosecute the officer – and on what charge – by Christmas 2009.

The CPS has given various explanations for the delays, and claims it has had to return to the IPCC for clarification several times on different issues.

It is also understood that there have been complications surrounding the evidence of an expert witness.

The IPCC itself was late in mounting an inquiry, claiming there was nothing suspicious about the death for almost a week until the release of footage of the incident obtained by the Guardian forced a U-turn.

GMC hearing

Patel is facing the General Medical Council accused of giving questionable verdicts on four causes of deaths, several of which later turned out to be suspicious.

Dr Carey, who carried out the second postmortem examination on Tomlinson, today criticised Patel at the GMC, where Patel's disciplinary hearing began last week.

The hearing focuses on his actions during postmortem examinations of a four-week-old baby, a five-year-old girl and two women.

The panel was told that Carey had been called to examine the exhumed body of the five-year-old after concerns were raised about the initial recorded cause of death.

Patel had concluded there were "no significant marks of violence". But Carey said the death was due to a "severe head injury" likely to have been inflicted by the "actions of a third party".

At the start of this afternoon's evidence, the panel was told by the hearing's legal adviser to ignore any of today's media reports involving Patel, who denies misconduct.