RAYMOND Easton has advanced Parkinson's disease and can barely dress himself in the mornings, let alone drive. But in April 1999 he was arrested for carrying out a break-in 200 miles from his home in the middle of the night.

According to Greater Manchester Police, a DNA sample taken from blood found at the scene of the burglary matched his own at six points - a "37-million-to-one chance".

Mr Easton, 49, from Swindon, had never even been to Bolton, where the burglary happened. But four months later he was charged. "They said it must have been me because the DNA said so, " Easton says. "They wouldn't even entertain the thought that they had made a mistake."

The case was later thrown out of court after a more rigorous test. It showed that Easton's DNA profile, held on the police database after an earlier family dispute, failed to match the crime scene DNA at a further four points of identification, known as loci, along the DNA molecule.

Six years later, Mr Easton is still the highest-profile victim of a DNA "mismatch". But that could all be about to change, according to a leading forensic expert.

Many more innocent people could become suspects for murders, rapes and other serious crimes because of the new highly sensitive DNA profiling techniques employed by British police, according to Professor Allan Jamieson, director of the Forensic Institute, Edinburgh, and the former head of Lothian and Borders Police forensic science lab.

Jamieson believes that "low copy number" (LCN) DNA analysis is vulnerable to contamination and could lead to "another Shirley McKie".

Britain is the only country in the world where police forensic scientists employ the highly sensitive LCN technique. It allows crime scene investigators to detect invisible amounts of DNA from a surface which a suspect has brushed against or merely breathed on.

There is no longer any need for blood, semen or saliva. A single skin cell is enough to create a DNA profile. Police commonly use LCN to reexamine unsolved "cold cases" - where an old crime scene sample did not yield enough DNA to create a profile.

But LCN is so sensitive that it can detect the DNA of persons who may never even have visited the scene, let alone committed the crime.

Jamieson explains: "DNA carries great kudos in the public eye and in court. When people hear the police have made a DNA match they think, 'oh, he must have done it'. But your DNA can get to places you've never been. If you shake someone's hand, they take some of your cells with them. And (with LCN) we are now in the realm where a single cell is enough for police to create a DNA profile.

"I fear innocent people will be mistakenly identified as suspects as a consequence of being on this database."

The Association of Chief Police Officers in Scotland (ACPOS) is lobbying the Scottish Parliament to pass a law allowing police to retain the DNA profiles of everyone they arrest, even those who are later released without charge. The same law has been controversial in England and Wales, where 124,347 innocent people have been added to the database since 2001, including 24,000 juveniles and one-third of the black adult male population.

Jamieson says: "Police will be knocking on your door, asking you, 'Have you been at a crime scene?'You might answer truthfully, 'no'. But will the police believe that? In court, the requirement for additional, corroborative evidence may be reduced if we believe implicitly in the DNA results.

"I fear that if we do not introduce safeguards, we are in danger of a serious error which will shatter public confidence in the whole system of using DNA as evidence.

Jamieson believes police must begin exercising greater contamination control at crime scenes.

But with other cases, it is of course, already too late.

"Many, if not all, of these old cases occurred before DNA forced a rethink of the possibilities for contamination of evidence. Exhibits were collected with little regard for who was handling them. It is inevitable that as a consequence, they will be contaminated with the DNA of, for example, police officers and lab technicians".

"But with low-copy number DNA, there is often no way of verifying contamination as there is no second sample test."

It is often said that "those who have done nothing wrong should have nothing to fear" about having their DNA profile held on a database. But in the light of cases such as Raymond Easton's, the commons science and technology committee has called for the introduction of an independent watchdog to investigate and regulate how all forensic science is used in court.

"I know some people have fears over the impact on human rights, " says Paddy Tomkins, ACPOS spokesman on the DNA database, "But I believe the benefit to society of holding on to such samples outweighs those concerns."

To make his case, Tomkins cites home office statistics that, since 2001, when the law changed in England and Wales, there have been 10,000 offences where crime scene DNA has been "matched" with DNA of persons who were not convicted.

But how many were simply matches with innocent passers-by? No-one knows. That information is, oddly enough, confidential.