SCIENTIFIC evidence is vital to more criminal cases than ever before, but it is also increasingly complex.

In any justice system worthy of the name, such evidence must not only be examined by the prosecution but also be able to be tested by the defence.

In Scotland, forensic scientists engaged by defending solicitors are so restricted in how they can access the evidence that it raises the question of whether the system is operating fairly. In other parts of the UK and in other advanced countries, scientific experts are sent or can make copies of the official record made by their opposite numbers working for the prosecution. Here, the Scottish Police Services Authority (SPSA), which owns and runs the laboratories, refuses to allow copies, requiring scientists to make notes. This is not only time-consuming but, at £100 an hour, costs the Scottish Legal Aid Board (Slab) a considerable sum.

More fundamentally, however, by preventing the original case files being sent to other experts, the practice can prevent a proper scrutiny of the evidence in cases which require particular specialist knowledge. The police not only decide how to test the original evidence but can also bring in outside experts as they deem necessary. However, above a threshold of £800, the defence must obtain quotes and use the cheapest available expert. This is intended to comply with the principle of best value in public contracts but breaches that of equality of arms before the law.

The cornerstone of justice that an accused person is innocent until proven guilty is rendered meaningless if he or she cannot examine and challenge the evidence on equal terms with the prosecution. That is the most important issue here. But the extra and unnecessary cost of the system as it is currently operated in Scotland is an additional scandal. At a time of public protest by lawyers at changes to the legal aid system designed to save nearly £4 million a year, the cost to the legal aid board of accessing forensic evidence must not escape scrutiny. That it amounts to money being transferred round the system from the legal aid budget to the police budget at unnecessary administrative cost is shockingly wasteful at a time of acute pressure on public spending. Some sort of ceiling on costs is necessary but these could be kept within limits by allowing electronic copies of the evidence to be available to recognised experts.

Scots law has already been found in breach of the European Convention on Human Rights in the Cadder judgment, which gave suspects in custody access to legal advice. That should prompt additional awareness of the potential for further challenges to the way the Scottish legal system operates.

An inability by defence experts to verify the testing and results of forensic evidence denies Scots accused of crime the rights extended in other comparable judicial systems. That is an unacceptable constraint on justice which must be rectified.