How a crusader against abuse provoked the anger of accused parents

Near the beginning of "A Very Dangerous Doctor", next month's Cutting Edge documentary on Channel 4, there are a few seconds of grainy footage that are among the most shocking to be broadcast on TV.

They show mothers smothering their youngsters – one using a T-shirt to stop her child breathing, another holding a hand over her child's mouth and nose and a third lying prone across her child's face while its tiny arms and legs thrash frantically as it struggles for air. They were taken by covert video surveillance of women whose babies were being investigated in hospital for breathing difficulties.

The secret videos, introduced by Prof David Southall more than a decade ago for detecting abuse, proved doctors were looking in the wrong place. The problem lay not with the children but the parents.

Dozens were convicted as a result and their children removed to safety. Dr Southall was hailed by colleagues for "thinking the unthinkable" – that parents could harm their children. He became an expert in Munchausen's syndrome by proxy (now called fabricated or induced illness), in which mothers injure or poison their youngsters to gain doctors' attention.

But like many doctors working in child abuse, he soon felt the anger of parents who claimed they were wrongly accused.

For more than a decade they have campaigned against him and his colleagues, filing thousands of complaints and triggering investigations by hospitals, the GMC and police.

Four appear in the Cutting Edge documentary, including Justine, suspected of smothering her two-year-old daughter Rosie. The child had been kept in hospital, hooked up to monitors for five days with nothing to do but watch a Thomas the Tank Engine video over and over again.

"To me that was tantamount to child abuse," Justine says. But she lost her daughter, who was taken into care and not returned for a decade. She has since campaigned for more than a decade to have Dr Southall struck off.

He remains unmoved. "The lies told by parents doing this to their children are continuous," he says. "I remain of the view that I did the right thing for all the children involved."

There are 47 cases pending against him, according to the film, (although the GMC said it did not recognise this figure) and the Medical Defence Union has spent £750,000 defending him – and is still doing so.

In 2004 he was found guilty of misconduct by the GMC and suspended from involvement in child protection work for three years after he accused the husband of solicitor Sally Clark of murdering her children on the basis of a TV interview he had given. Following that verdict, 53 UK paediatricians wrote to protest that the GMC verdict "conflicted with child protection laws and guidance for professionals".

Filmmaker Leo Regan says the dispute between Dr Southall and parents is unlikely ever to be resolved.

But in a tribute to his skill, both sides say his documentary, which they have seen, is fair.

Dr Southall's critics say he did not just test the boundaries, he crossed them and was overzealous in his conviction that children must be protected at all costs. Like many pioneers attacked for their beliefs, he deals in absolutes and is unrepentant. Hope now rests with the GMC's working group and the new guidance it is due to provide to doctors involved in child protection. GMC chief executive Niall Dickson says: "We need to build confidence in what will always be a difficult area of practice."

'A Very Dangerous Doctor' will be shown by Channel 4 on 12 May at 9pm