When, in 1978, Derek Brushett took up his post as headmaster of the Bryn-y-Don approved school in Dinas Powys, south Wales, the boys naturally referred to him as "Basil" Brushett. Then some wag noticed an implement in a hardware shop, and they all began calling him "Bendy" Brushett, which was even funnier. But the name also carried connotations about his behaviour. Brushett is now serving 12 years' imprisonment for serious sexual offences against those in his care.

He had become a social services inspector by the time of his arrest, and some described him as the most prominent catch netted in the trawling operations conducted by British police forces over the past decade. Others, however, describe him as the most prominent victim of such police methods.

Criminologist Dr Bill Thompson of Reading University has examined all the papers in the Brushett case. "Every teacher on the planet has been subject to rumours at school," he says. "In Derek's case, it's quite clear that rumours floating round at school back then have now been used to assemble a criminal case. It was 'Bendy' Brushett, and then it was 'the bendy-boys'. You can imagine how it all happened. Now each accuser is putting himself into the rumour mill."

Although ostensibly one of the country's most unconscionable child abusers, Brushett remains highly regarded in his home village of Dinas Powys. The depth of concern over his case and others was highlighted last month when the parish hall there was filled for one of the now regular conferences of Fact - Falsely Accused Carers and Teachers.

Fact is one of 18 campaigning organisations throughout the country set up to redress the injustice suffered by those who, they claim, have been wrongly convicted in abuse cases. Now, an all-party parliamentary group for abuse investigations has been established, and held its first meeting last week. Chaired by Crosby MP Claire Curtis-Thomas, its 50 signatories in both the Commons and the Lords include former Crosby MP Baroness Shirley Williams.

"The purpose of this group is not to mount campaigns for individuals," says Curtis-Thomas. "It is to scrutinise the procedures that actually lead to convictions. We want to begin to question the validity of the process when individuals are convicted on verbal testimony alone without any corroborating evidence. Elements of the pre-trial process are open to abuse."

There are, broadly, two kinds of cases, which, it is claimed, can lead to wrongful convictions: "domestic" cases, in which either a family rift or psychological problems may lead to bitterness and unfounded accusations; and "trawling" cases. A trawling investigation is the inversion of standard police practice. Normally, the police are confronted by a crime and need to produce suspects. In trawling inquiries, the police have a suspect and need to produce crimes.

This type of investigation was made possible by two key changes in the law. In the case of DPP v P in 1991 the Lords dispensed with the requirement that a variety of charges could be brought against an alleged abuser only if there were "striking similarities" between the allegations. The previously held view that a predator would have a particular modus operandi was overturned.

Additionally, a vital safeguard for the defence disappeared in 1994 when the Criminal Justice and Public Order Act removed the need for judges to give warnings to the jury about the absence of corroboration, which thereby lowered the threshold for proof in these cases.

So when a historic allegation is made by a former resident of a care home or institution, police can "trawl" other past residents by public announcements, inviting them to come forward, or by sending out letters indicating that they will be interviewed as part of an ongoing investigation.

Those former residents will now be men, many of whom will be in prison. They will immediately understand that the investigation concerns allegations of abuse. They will also know that, if they jump on board, they will be entitled to thousands of pounds in compensation by going to the criminal injuries compensation authority. The more serious the allegations, the more compensation they will receive. They will also know that it is all but impossible to disprove their allegations.

"I do not like the practice of trawling," said Lord Lucas in a Lords debate last month. "It is too much of a temptation, particularly where people being asked are themselves criminals or damaged people for one reason or another. It invites false accusation, especially when there is no penalty for making a false accusation."

One of the problems with accusations of this kind, in a courtroom context, is that their very implausibility renders them plausible; jurors consider the allegations so disgusting, so unnatural, that they cannot have been invented and so must be credible.

Yet although compensation may be the most obvious factor in promoting untrue accusations, it is not the only one. Gisli Gudjonnson, a professor of forensic psychology who was formerly concerned with the problem of false confessions made by suspects under police questioning, is now worried about the equally serious problem of false allegations.

"We need to distinguish between allegations that are genuine and those that are not," he explains. "It's not just that people are vulnerable to police questioning; there are also internal vulnerabilities. Many accusers are very low on suggestibility: they're bright, imaginative individuals. People imagine that this [abuse] has happened to them. It fills an internal need and helps them explain why their lives are so screwed up.

"We're doing research into what makes judges believe these people. It's clear that if there is more than one complaint, the judges believe that corroborates it and so it's convincing. But these cases are particularly risky because you have to avoid contamination; you get people communicating, or police officers inadvertently passing on what others have said."

Solicitor Chris Saltrese, whose father was headmaster of a care home, is handling a number of convictions resulting from trawling operations. The first such case that came to him was that of Terry Hoskin, former head of a community home in Widnes, who was convicted on 21 counts of physical and sexual abuse of boys in his care.

"I lived on site at a home," says Saltrese. "I knew the ethos of these places - I knew what the boys were like, I knew what the staff were like. When I read the papers in the Hoskin case, I thought, 'No, this doesn't feel right.'

"I also thought it was systemic - you could see Hoskin being applied elsewhere - and that's what has happened. There are now probably 20 convictions that I personally know of that I consider to be unsafe."

One of these cases is that of Roy Shuttleworth, formerly a residential housemaster, who was sentenced to 10 years' imprisonment in 1996. He was convicted despite the fact that one of the complainants against him actually had a previous conviction for a conspiracy to gain criminal injuries compensation by deception. Two months after Shuttleworth was refused permission to appeal, his wife died of a heart attack. He had to attend the funeral in handcuffs.

Trawling for complaints against suspects is particularly productive among emotionally disturbed former residents of care homes. "The definition of a suspect is one matter I've raised in a parliamentary question," says Curtis-Thomas, "because we think that in some circumstances every careworker is regarded as a suspect, irrespective of whether there's any evidence against him."

The amassing of allegations has become almost routine. Responding to inquiries from Doreen Strettle - the wife of convicted careworker Barry Strettle, whose case goes to appeal in December - one police force, Cheshire, has acknowledged that nine investigations into care homes since 1990 have led to allegations from 738 former residents against 315 different men.

One of the great sadnesses of this issue is that it is people who were formerly doing one of the most difficult tasks required by society (looking after emotionally disturbed children) who now seem to be targeted.

"The people who are subject to false allegations were usually the most conscientious members of staff," says Thompson. "They are the ones who did the work, who did the extracurricular activities. These people have in a sense set themselves up by being close to the kids and doing the real job they had to do, which was acting as surrogate parents. It's always the nice people who get accused."

See also:
False Allegations Support Organisation
Eddie Hampton case, MOJUK
Phil Taylor case, MOJO

Rebecca Williams Rigby remembers the moment she knew her father was going to prison very clearly. "He said 'how can I prove my innocence?' and I just hugged him and said 'you can't, Dad'. Then I knew for certain that he wasn't coming home."

Basil Williams Rigby will not be coming home for some time. He is currently in HMP Wakefield, doing a 10-year stretch for abusing children in his care over 20 years ago, leaving his family to protest his innocence.

While they search for some small scrap of fresh evidence that might get him out - a hopeless task after all this time - Basil reflects on the poor quality of the evidence against him and the fatal weakness of his efforts to challenge it.

If he would attend the prison workshop designed to help him confront and resist his paedophilia he would be out a lot sooner. But since he is protesting his innocence, enrolment in these sessions would amount to a false admission of guilt. He prefers to do the full stretch.

If he had been charged with murder, fraud or GBH the evidence against him would almost certainly have failed to convince a jury beyond the 'reasonable doubt' that is supposed to protect us from miscarriages of justice. But an allegation of child abuse is different, especially one that is 20 years old.

After 20 years there is no forensic evidence to strengthen a case. And since abuse is a furtive, behind-closed-doors crime, there is precious little corroboration in witness statements collected by the police.

But that does not seem to bother juries in today's hysterical climate. According to support group False Allegations Against Carers and Teachers (Fact), there is a 90% conviction rate for alleged sex abusers.

That compares with a conviction rate for rape of just 9%. Chris Saltrese, a solicitor based in Southport who has worked on a number of sex abuse cases, says: "Juries think that there is no smoke without fire and they will convict on the flimsiest of evidence. Who wants to be responsible for letting a paedophile back onto the streets?" As a result of this, he says, "there are at least 20 innocent men in prison in the north west alone".

The police reinforce poor quality evidence by collecting a large quantity of it. Some former care workers face dozens, if not hundreds of statements, collected by the police in a series of 'trawling' operations going back decades. A single investigation begun in 1997 resulted in 66 arrests and 20 convictions. Officers collected 759 complaints involving 358 suspects in the first three years alone. And there are 80 other investigations involving 31 other police forces around the country.

A former police officer involved in one such operation told us that this reliance on quantity can be dangerous - especially since witness statements are not taped so there is no evidence that they have been collected appropriately.

"I do believe now that people are going and knocking on people's doors and asking them ' were you abused?' by the way so-and-so's abused - did Mr so-and-so abuse you and these are the sort of things that are being put to them," he said.

He believes that the possibility of compensation actually generates some complaints. "I do know that a certain amount of compensation is being mentioned - sometimes up to £100,000. And a lot of the people who are in jail now, they were at these homes - they were never abused - are looking at this and thinking 'hang on - there's a lot of compensation for me to earn here'."

There are guidelines to prevent officers from introducing the identity of a suspect to a witness or mentioning compensation if a witness helps them - but there is evidence that these guidelines are sometimes breached.

No one doubts that there has been sex abuse in our children's homes. Of the 21 cases first brought to court in Merseyside, 19 resulted in guilty pleas. But can we be sure there are enough safeguards in the system to prevent miscarriages of justice as well as protect damaged and vunerable children? Now we are steeped in the hysterical atmosphere of tabloid newspaper 'outing' and mob 'justice' we may no longer be able to consider such cases safely.