It was the first time Rosalie O'Brien had let her nine-year-old son, Peter, cross the road on his own. She held back a few yards with three-year-old Sarah in her pushchair, as he tentatively stepped on to the pedestrian crossing. The first line of traffic on the busy road in Feltham, Middlesex, stopped for him.

Adam Gibbs was in a hurry. It was his last week with the delivery company before returning to university. He was in the inside lane when the traffic came to a halt. He thought it was the bus at its stop and pulled out to overtake, his foot hard down.

Peter never had a chance. The van hit him so hard that he flew high into the air and landed 40 yards away. He survived 21 hours but died without regaining consciousness.

The accident, in September 1990, was the second tragedy to befall the O'Brien family. Ten months earlier, Rosalie's husband, Patrick, had died of a heart attack aged 39. The loss of both of them was unbearable.

Mrs O'Brien reacted as many relatives do, wanting to ensure that the driver was properly punished. She went to the police to give a statement soon after the funeral. But this was to be the first of many contretemps with the police. No, said the inspector, you are much too upset to make a statement now.

'I was perfectly able to give the statement,' she says. It was the beginning of her suspicions that Peter's death was not being treated as a serious matter.

Mrs O'Brien knew that charges had to be laid within six months of the offence, and as the police had intimated that Mr Gibbs would be charged with 'causing death by reckless driving', she rang to check on this just before the deadline. She found he was only facing prosecution on four less serious offences that amounted to driving without due care and attention.

Mrs O'Brien drew up a petition in order to get the Crown Prosecution Service to change its mind. She wrote and, a week later, the CPS agreed. Mr Gibbs was to plead not guilty.

But the feeling that the police were not interested persisted. Mrs O'Brien was told that 'this created an awful lot of paperwork'. She had hoped the trial would take place as soon as possible, but it was postponed to allow Mr Gibbs to finish his exams. The inspector sympathised with Mrs O'Brien but said: 'You have to remember he's studied hard.'

The jury took little time to convict Mr Gibbs. Although the offence then carried the possibility of five years' imprisonment, the judge imposed a pounds 500 fine, pounds 600 costs and a four-year ban, saying: 'Compared to most young people I have to deal with, he is an excellent young man.'

Mrs O'Brien has been left deeply angered by the role of the police. A couple of weeks ago, a superintendent took down full details of her complaints. But she still feels there are some basic things that could be done: 'How come, when a car has been stolen and the driver kills a pedestrian, they are charged with manslaughter, but if the car has been driven legitimately, they are not?'

The CPS says this is not the case. A spokeswoman said: 'Sometimes the police bring manslaughter charges, but we change them to causing death by dangerous driving.'

Mrs O'Brien did not want Mr Gibbs to go to prison. 'But,' she says, 'he didn't ever say I'm sorry. He treated it as a bit of inconvenience, a hiccup. For me and Sarah, it's a life sentence.'