Professor Allan Jamieson, who runs The Forensic Institute in Glasgow and is a former head of forensics at Lothian and Borders Police, said they are routinely charging defence lawyers £100 an hour to access evidence for use in court cases.
He said this was driving up the cost of legal aid, which Justice Secretary Kenny MacAskill plans to change in an attempt to save money.
Mr Jamieson said labs in other jurisdictions shared notes, but the Scottish Police Services Authority (SPSA) insists vital paperwork can only be viewed in the presence of its own scientists. Those acting on behalf of the accused cannot make copies.
In a letter in today's Herald, Mr Jamieson, whose business provides expert witnesses to defence lawyers, said his profession was becoming increasingly frustrated by what he called an "abhorrent practice".
He said: "Our work involves reviewing scientific evidence in criminal cases.
"In other UK and international jurisdictions we receive or make copies of the lab notes and records of the prosecution.
"Not only does the SPSA charge for 'supervision' of our scientists even looking at the notes [because they refuse to allow copies], they charge the defence, and hence the Scottish Legal Aid Board, £100 an hour for the privilege.
"Who is happy to pay to see the evidence against them?
"One small practical way in which we can save money is to encourage the Scottish Government to get the SPSA to abandon this abhorrent practice that simply moves public money from one place to another, and allow the defence copies of their notes.
"The argument about legal aid should not be about spending more money, it is about spending what we have more wisely."
Mr Jamieson was writing as criminal defence solicitors and the Scottish Government clashed over cuts to legal aid.
Defence lawyers refused to work on Tuesday, the day after a St Andrews Day bank holiday weekend for court staff.
It formed part of a "strike" against cash-saving reforms they argue threaten access to justice rights.
Mr MacAskill plans to force anyone with a disposable income of £68 or more to pay something towards their legal fees. Lawyers claim it undermines the right of an accused person to have the best defence not based on cost.
The SPSA says it is committed to allowing defences "consistent, fair and transparent access to productions and specific information held by the organisation".
It says it allows defence teams – and expert witnesses such as Mr Jamieson – to precognose its forensic scientists for free provided this takes place at the witness's normal place of work.
The body, soon to be merged into Scotland's single force, does not allow unfettered access to the notes of forensic scientists on everything from DNA to fingerprints. Labs in England and Wales, which are private, rather than the police, share such notes.
A spokeswoman for the SPSA said: "We have a very different legal system in Scotland and have an agreed defence access policy to which we comply.
"I can't comment on why other jurisdictions don't apply the same policy."
Tom Nelson, Director of SPSA Forensics and a former colleague of Mr Jamieson, defended charges to defence witnesses.
He said: "Charges apply in instances where SPSA scientists are required to undertake additional work for defence access, for example, preparing samples for additional examination.
"Charges are calculated based on organisation costs, staffing time and any time spent in the preparation of data or administrative work.
"Applying charges is not a new policy and has been applied for a number of years to ensure that the finite amount of money we have to spend is able to sustain the core services we provide."