Footage from G20 protests gives fresh angle on attack Channel 4 News

The family of Ian Tomlinson face a three-year wait for an inquest into his death, according to legal experts, who say that pressures on the coroners' system are "frustrating the grieving process" for victims' relatives.

The claim is likely to dismay critics of the police, who have expressed concerns about how Tomlinson's death is being investigated. According to the first post-mortem examination, Tomlinson, a 47-year-old homeless newspaper vendor with a drink problem, died after suffering a heart attack while caught up in last week's G20 protests.

Video footage appears to show a riot policeman hitting Tomlinson with a baton and shoving him to the ground. There are also claims that Tomlinson may have been bitten by a police dog, and that he came into contact with the police on several occasions before the alleged assault was captured on video. There are concerns that the alleged assault - which took place as Tomlinson was trying to get back to his hostel - may have contributed to his heart attack. A second post-mortem was carried out on Thursday.

The footage has raised questions about police tactics for dealing with protesters, and in particular the strategy called "kettling", which involves herding protesters behind cordons.

Boris Johnson, the London mayor, is expected to come under pressure over the broader tactics adopted by the Metropolitan Police during the protests. Members of the Metropolitan Police Authority are expected to challenge both senior officers and the mayor's office over what was agreed about handling violence during the summit.

Jenny Jones, a Green member of the London Assembly who has led calls for a review of "kettling", said that she would join Labour and Liberal Democrat authority members at an informal meeting on 23 April to demand answers.

She said a key question would be what Johnson's office had known or agreed about confrontation with the protesters. "I am very curious - because we heard all these phrases [from the police] about 'we are going to be up for it' - to know what the meetings were like with the mayor's office. I just wonder if the police were told to keep it calm," said Jones.

Legal experts said last night that a full independent inquest is unlikely to take place for years. "From our experience of deaths involving police contact, delays of two to three years are not uncommon," said Deborah Coles, director of Inquest, the organisation that represents the families of people who die in custody.

"While you want to ensure there is a thorough investigation, a lot of the delays are caused by pressures on the coroners' system," Coles said. "The system simply does not have the ability to cope with the outstanding caseload."

More than 300 protesters marched in silence through London yesterday to lay flowers at the spot where Tomlinson collapsed. Paul King, Tomlinson's stepson, told marchers: "We are hopeful that the IPCC [Independent Police Complaints Commission] will fulfil its duty to carry out a full investigation into his death and that action will be taken against any police officer who contributed to his death through his conduct."