The Forensic Science Service, a Home Office agency, was closed in 2012. More than 1,000 scientists lost their jobs and either left the profession or moved to new providers.

A recent Guardian article highlighted concerns raised by independent forensic scientists about the new charging practices after they faced demands for payment before being allowed to examine DNA, firearms and other key material in criminal cases.

The paper reported that in some cases companies charged experts hired by the defence up to £800 a day for access to firearms held in laboratories. The introduction of the charges is a result of firms exploiting guidance from the Home Office's forensic science regulator.

In a footnote providers were told: "It would be reasonable to charge the defence for any use of facilities or equipment, or for the provision of copies of documents in hard copy or electronic form, under the disclosure regime."

But, as Prospect negotiator Steve Thomas said: "It was entirely predictable that in a commercial and shrinking market, forensic science providers would exploit the regulator's guidance to develop income streams in a way that the FSS never did, restricting access for those who need it most.

"FSS previously provided free access to labs and other facilities, for example photocopying papers and sending them on, at nil cost. As FSS was the main provider others did the same.

"These costs will now most likely fall on the government's Legal Aid Agency, which pays for the representation of many defendants who appear in criminal courts."

Thomas added that it was symptomatic of the lack of foresight demonstrated throughout the closure process, which ignored concerns over access to evidence, techniques and sharing research and development data. "We now know that the government did not even consult its own chief scientific adviser to the Home Office."

The Guardian report also described a recent court ruling ordering a major provider, LGC Forensics, to supply exhibits and DNA profiling results to defence experts in a sex case within 48 hours after an expert was asked to enter into a 'credit agreement' before information would be handed over.

Finally, the article quoted a spokeswoman for LGC Forensics, who said requests from the defence to examine forensic material were 'very rare'.

"When we are asked for information this is usually because a party in the case wants to check the work we have done. They will have to come to our laboratories. They will have to be supervised and that is a cost we have to charge for.

"In the past that would have happened when the FSS existed. Perhaps the cost would previously have been borne by the taxpayer. If requests for information are being asked for by someone else [other than the police] then we need to make sure we can be paid ... This is supported by the forensics science regulator guidelines."