Dr Zakaria Erzinclioglu, a senior research associate at Cambridge University and the director of the Forensic Science Research Centre at Durham University, claims, in a book, that "new and unhealthy pressures" have been brought to bear on forensic scientists because of the pressure on police to secure convictions. The result, he says, is that he has witnessed 48 miscarriages of justice in one year.

The allegations, made in his book Maggots, Murder and Men, are being taken so seriously that Lord Justice Auld is examining them in his review of the court system and will report to the Lord Chancellor in January. Dr Erzinclioglu, who has worked on investigations into murder cases for more than 20 years, is lobbying for an independent state-funded body to administer the pay of forensic scientists.

At the moment they are paid by the lawyers using them as witnesses - with the result, he says, that they are encouraged to lie in order to satisfy their paymasters. Dr Erzinclioglu said: "Forensic scientists should not be subject to financial or emotional pressures and their independence must be guaranteed and defined in law so that, like judges, their neutrality and objectivity can be upheld in every way.

"Unfortunately at the present time forensic science evidence is paid for by people who are, by the very nature of the system, biased, even if they are sincerely trying to arrive at the truth. Police officers and lawyers are interested but not, with the best will in the world, disinterested, parties."

Dr Erzinclioglu said that he has been pressurised on a number of occasions by the police and lawyers to give the evidence that they want to support their case and because he refused he has not been employed by those people again.

He said: "One solicitor asked me to make up an answer. I know the kind of pressure the police bring to force you into a certain kind of investigation and there can be financial pressure for special witnesses to say certain things because their livelihood depends on it.

"Each forensic scientist is a narrow specialist and he needs all the cases that come his way, and if you fail to satisfy a particular lawyer he is not going to consult you again."

Dr Erzinclioglu specialises in examining the maggots on corpses as a means of determining where and when someone was killed. As the lifetime of a maggot is only five days, it can often be the most accurate way of pinpointing the time at which someone has died.

In addition, because there are 500 different species of the grub in Britain, and given that corpses are often moved from one location to another, they can also form vital evidence in indicating where someone was killed.

Dr Erzinclioglu has a doctorate in maggots, but he said many of the "experts" brought in by the police and lawyers are charlatans: "There is nothing to prevent a person who is totally unqualified as a scientist from practising as a forensic consultant."

Stephen Kramer, QC, the chairman of the Criminal Bar Association said: "The best experts are the independent ones and you have no guarantee by having just one expert - as would be the case if this new system was introduced - that you will get the right result. Having two experts is frequently quite useful as a cross-check and enables the jury to be able to conclude whichever way they want. The experts, after all, frequently agree."