The survey, undertaken by the New Scientist, showed that most also believe that switching to private and in-house police labs will reduce impartiality in interpretation, and therefore accuracy, of evidence.

The findings reopen questions about bias in forensic science, with nearly a third of respondents admitting they sometimes feel pressured to produce a particular result, while three-quarters say they sometimes have insufficient time to evaluate cases.

Circulated via the professional networking site LinkedIn, the survey attracted 365 responses with the majority from FSS employees although 65 respondents were from private and police labs.

Of the 21 police scientists who took part, 15 said the switch would make it harder to interpret evidence. "More and more cases are being broken into component parts and incomplete examinations are requested of private laboratories because in-house police labs believe they are saving money," said one respondent from a private lab.

"This makes the interpretation of the evidence within the context of the whole case very difficult because the scientist does not have a complete picture."

One police scientist said that breaking up services could make it easier for scientists for the defence to challenge cases because key questions, such as what body fluid DNA came from, may no longer be asked.

New Scientist also highlights numerous examples in the US where lab analysts have felt under pressure to produce particular results  – and claims UK analysts face similar pressures:

• 28 per cent said that they sometimes or always felt pressured to produce a particular result
• 75 per cent said they had insufficient time to evaluate a case properly
• 83 per cent - he overwhelming majority - felt the issue would get worse over the next five years.

The survey followed another recent report by the magazine illustrating how DNA analysts can reach very different conclusions about the same evidence raising the danger of contextual information about a case colouring judgement.

While those managing private and police labs have been quick to refute the claims, Prospect negotiator Steve Thomas said: "We share the concerns of those surveyed and we have expressed them on a number of occasions throughout this process.

"Ministers made a dogmatic decision that we feel will risk certain elements of the criminal justice system."

See the report in full as well as a selection of comments from the forensic scientists who took part in the survey.