The widow of Ian Tomlinson, the man who died at the G20 protests, has launched an emotional attack on the director of public prosecutions, accusing him of letting her down over his failure to decide whether the officer who assaulted her husband should be charged with manslaughter.

Julia Tomlinson accused Keir Starmer, who heads the Crown Prosecution Service, of misleading her family. Her comments come days before the anniversary of the death of Tomlinson 12 months ago, and amid growing concern that the police have escaped largely unscathed from their controversial handling of last year's protests in the City of London.

Figures obtained by the Guardian show that although almost 300 complaints were lodged about police behaviour during the G20 demonstrations, not a single officer has faced serious disciplinary action.

Tomlinson, a 47-year-old newspaper seller, had been walking home from work through the protests in the City on 1 April when he was attacked from behind by a member of the Metropolitan police's territorial support group (TSG).

Last August the CPS was asked to consider whether the officer should be charged with manslaughter and, weeks later, Starmer promised swift action. "My view on these things is we should move quickly," he said, adding that he hoped for a decision "in a few months". CPS officials later told the Tomlinson family they could expect a decision by Christmas.

"Keir Starmer has let us down personally," said Julia Tomlinson. "Why did he say there would be a decision around Christmas? Why are we still waiting? My kids need to move on from this. They're left without a dad now and their lives have been turned upside down over the last year, especially the four girls. He doesn't seem to realise the pain we're going through."

She added: "We feel like there was a cover-up from day one, and we didn't see it because we were nervous about the police. Now a year on it still feels like all of that is still going on. If it had been someone on the street, a civilian, who had pushed and hit Ian just before he died, and it was all caught on video, surely something would have happened by now. The officer needs to go before a jury. Let them decide what should happen to him."

Last night the CPS said that delays were due to outstanding clarification required from the Independent Police Complaints Commission (IPCC), which initially investigated the death. "In December the CPS asked the IPCC to undertake some further inquiries. Having received that material, in February the CPS asked the IPCC for clarification of further evidence that is crucial to the issues in this case."

Human rights campaigners and MPs will join the Tomlinson family near the Bank of England on Thursday to lay flowers near the spot where he died. They plan to release a letter complaining about the "intolerable" inaction over his death, which they say raises serious questions about the police complaints process.

While a large number of officers were the subject of complaints after the G20, the number of protesters to have been prosecuted has been small in comparison with other major demonstrations.

Data held by the CPS shows that seven members of the public have so far been convicted of violent conduct, criminal damage and public order offences at or during the demonstration, including a handful who were identified as having taken part in the ransacking of a branch of the Royal Bank of Scotland. A further eight G20 prosecutions are pending, while two resulted in acquittals .

Prosecutors dropped charges in their largest case, which involved 11 members of the Space Hijackers, an anarchist group whose members arrived at G20 protests in a tank, dressed in police-style helmets and boiler suits. The theatrical activists, some wearing red stockings, were arrested and later charged with impersonating police officers. They are suing the Met for wrongful arrest and false imprisonment.

However, hundreds of officers have been forced to explain their actions after complaints from the public. In total the IPCC received 296 complaints about police behaviour, and decided to independently investigate six.

They included the Tomlinson case, and that of a 23-year-old woman who was told by a doctor she may have suffered a miscarriage after being kicked, punched and pushed with shields and batons. The IPCC found that despite the woman's serious injuries, she was not allowed out of a police cordon for more than five hours.

Another case involved a TSG sergeant, Delroy Smellie, who went on trial this week accused of assaulting a female protester at a memorial vigil for Tomlinson on 2 April. Footage posted on YouTube was played to Westminster magistrates court showing Smellie, 47, back-handing protester Nicola Fisher, 36, before striking her twice on the legs with his baton.

Fisher, who was described by witnesses as having been aggressive towards the police, failed to turn up to give evidence, while Smellie, who denies assault, said he mistook the camera and carton of orange juice the activist was carrying for weapons. A district judge is expected to hand down a verdict in the case next week.

More than 200 IPCC complaints – the majority – were forwarded to internal police complaints departments, which received supervision from the IPCC in about 60 cases. Some of those cases are still undecided, according to provisional figures obtained by the Guardian.

The data show that only a tiny fraction of complaints have been upheld, while several officers escaped with "words of advice" or written warnings.

Of the cases adjudicated by the Met's directorate of professional standards, the largest complaints unit, 195 were found to be unsubstantiated, withdrawn, dispensed with or otherwise discontinued, with only two substantiated. Both officers received written warnings.

Police reform campaigners argue that the failure to discipline officers has exposed an ineffective police complaints system that has led to a "culture of impunity".

In the four years leading up to the protests, for example, the TSG, the specialist unit of 730 officers at the centre of controversy after the G20, received more than 5,000 complaints, mostly for "oppressive behaviour". Of those, only nine were substantiated after an investigation by the Met's internal complaints unit.

In their defence, senior officers at the Met say they have learned from their mistakes at the G20, and there is evidence of a change in the tactics used at demonstrations.

Next week the Association of Chief Police Officers will release for consultation a "manual" for policing protests, setting out revised guidance for officers which emphasises their duty to facilitate peaceful protest.

Home Office ministers have also produced a code of practice, likely to be unveiled after the election.

Both documents seek to implement the far-reaching reforms called for by Denis O'Connor, the chief inspector of constabulary. His report last year into public order policing, a direct response to the G20 controversy, went further than many expected, warning that the police risked losing public support unless they adopted a more impartial, accountable style of policing rooted in "public consent".

O'Connor's findings echoed the conclusions of two parliamentary inquiries into the Met's handling of the G20, both of which made serious criticisms about some police treatment of protesters and journalists.

Already, the Met and other forces have adopted a "community-style" approach to protest, rolling back on the widespread use of forward intelligence teams, the units used to openly monitor protesters, and cutting down on the use of anti-terrorist legislation against activists. The protest movement is sceptical that the change will be lasting.

For the Tomlinson family, who have asked the public to gather at 11am on Thursday, it is not police reform that they will be calling for, but justice.

"In the last year there have been all these reports about policing protest but they don't seem to want to mention Ian," Julia Tomlinson said. "We just need a few more people on our side, to say Ian was a decent person who should have been allowed to walk home from work to watch the football that night. And for that to happen to him was wrong."

New York banker who shot the Tomlinson video

I was at Bank station again a few days ago, and it was quite strange being back. Naturally, the area had returned to normal as the shops were open, no one was throwing bottles and people were busily running around after work; it was as though nothing of consequence had happened.

I've been greeted by everything from admiration to derision for releasing this video to the public, as I put myself at potentially great risk by doing so. My motive was and remains to aid truth and closure for the family, though in hindsight it has become much more than that.

As the press coverage went on following the Tomlinson incident, it felt more and more clear that the circumstances of the death were being covered up. Given a few weeks, Mr Tomlinson would have become another tragic footnote and then forgotten. His family deserved more than that.

Of course, I could not know that the case would grab the nation's attention the way it did. I'm gratified that this incident sparked a needed policy review, as it became evident later that police aggression during public events was happening more often than it should.

I ask myself "What if?" a lot about that day. What if the police had not called in the dogs, which started a panic in the crowd? What if Mr Tomlinson were 5ft further away, just out of reach of the baton? What if, sensing danger as he got too close to the line, I had just walked 20ft up to him and escorted him to safety?

None of us could have known what was to happen, but those possibilities still weigh on me nonetheless."