Hundreds of criminal cases are to be reviewed because vital DNA samples may have been missed by the Forensic Science Service.
New DNA techniques have become available since 2001
The Association of Chief Police Officers has written to the 43 chief constables in England and Wales about cases that may need re-investigating.
Those under review fall within a five-year period between 2000 and 2005.
Shadow home secretary David Davis said it was important to maintain the quality of evidence.
A Home Office spokesperson said "a minimal amount" of cases were involved and that the situation would not have led to anyone being wrongly convicted.
Instead the cases involved situations where there was "no result" in DNA tests, which would have meant that potentially a guilty person was not convicted.
The cases would specifically involve Low Copy Number (LCN) DNA samples which involve tiny traces of DNA that have only been detectable with new techniques available since 2001.
The review relates to cases where the FSS analysed tiny samples of blood or saliva for a DNA profile, only to get a negative result when detectives had expected otherwise.
DNA evidence became traceable in very small traces of bodily fluids from 2000 following advances in testing techniques.
The FSS was apparently applying the new LCN technique in a different way, meaning its scientists may have missed DNA evidence that other private forensic laboratories could have identified.
The problem was highlighted by Acpo in November and the Home Office ordered the review when it was informed of the situation.
Acpo is now waiting to hear from police forces in England and Wales about any cases which may need revisiting - a spokesman said it expected a "prompt response".
A joint statement issued by the Home Office and Acpo said: "Towards the end of 2006 we become aware that a small percentage of DNA samples may need to be re-examined as a result of differences in the way forensic suppliers were using new techniques to analyse forensic material between 2000 and 2005.
"Acpo is very close to completing that work and has found no evidence that we should be concerned about standards being used today."
Shadow home secretary Mr Davis expressed concerns over a potential "fundamental failure".
He told BBC News 24: "DNA evidence is almost viewed as a silver bullet point by this government.
"Certainly it's insisting on increasing the DNA database, without the legal backing for it and so on, so it thinks DNA's very important, and rightly so, it is very important.
"Juries tend to believe it almost without argument. Therefore it's very important to keep the quality of that evidence up."
Liberal Democrat home affairs spokesman Nick Clegg said: "Given that the government is asking us to rely so heavily on DNA technology to detect crime, it is extraordinary that the necessary methods are not being deployed to use it to its greatest potential."
The FSS was involved with a controversy last year over "missed" clues in the Damilola Taylor murder investigation.
There were two blood spots and clothing fibres apparently not detected in the investigation at the time of the schoolboy's death.