What Is a Part 19 Expert Report - and Why Might You Need to Pay for One?
By MAJ Law on 21 September 2026
If you have been charged with a motoring offence and your solicitor tells you that an expert needs to be instructed under Part 19 of the Criminal Procedure Rules, you might understandably have a few questions.
What is Part 19? Why isn't my solicitor able to do this themselves? Why is there an additional fee? And, perhaps most importantly, could an expert actually make a difference to my case? These are questions we regularly receive from clients at MAJ Law.
The simplest explanation is this: Part 19 deals with expert evidence in criminal proceedings. Sometimes successfully defending a motoring allegation requires more than a legal argument. It requires independent scientific, medical or technical expertise to properly examine evidence relied upon by the prosecution. That work has to be carried out by an appropriately qualified expert, and their fee is separate from the legal fees you pay your solicitor.
What is Part 19 of the Criminal Procedure Rules?
Part 19 of the Criminal Procedure Rules governs the use of expert evidence in criminal cases. An expert is somebody with specialist knowledge who can provide an opinion on an issue that requires expertise beyond the ordinary knowledge of the court. Importantly, an expert instructed by the defence is not there simply to support the defendant's version of events. Their overriding duty is to the court, and their opinion must be objective and unbiased.
An expert report prepared for use as expert evidence must also meet specific requirements. Among other things, it should explain the expert's qualifications and experience, identify information relied upon, explain the facts upon which their opinion is based, address relevant ranges of opinion and provide reasons for the conclusions reached.
This is why obtaining expert evidence is considerably more involved than simply asking somebody for their thoughts on a case.
Why might an expert be needed in a motoring case?
Motoring prosecutions can involve highly technical evidence. This is particularly common in drink driving and drug driving cases, where the prosecution may rely upon forensic analysis of breath, blood or urine. For example, a drug-driving prosecution may appear relatively straightforward:
A blood sample was taken → a laboratory analysed it → the result was above the prescribed limit.
But that does not necessarily mean there is nothing further to investigate. Depending on the particular case, an appropriately qualified expert may need to consider the scientific evidence, laboratory documentation, testing process, analytical data or other material relevant to the reliability of the prosecution's evidence.
Part 19 provides the procedural framework through which expert evidence can be introduced and, in appropriate circumstances, through which material relating to the prosecution expert's examinations, measurements, tests or experiments can be requested.
The CPS itself has detailed guidance specifically addressing defence challenges in drink and drug driving cases and the procedure where the defence intends to instruct an expert.
Why can't my solicitor just check it?
This is one of the most important distinctions for clients to understand. Your solicitor is the legal expert. The forensic scientist, medical expert or other specialist is the expert in their particular discipline.
Your solicitor can examine the prosecution case, identify potential legal and evidential issues and determine whether expert evidence may be required. However, a solicitor cannot simply substitute their own opinion for that of a properly qualified expert on a specialist scientific or medical question.
Think of it in the same way as a medical case. A solicitor can identify that a medical issue is important to the defence, but that does not turn the solicitor into a doctor. Where specialist opinion evidence is required, an appropriately qualified expert needs to undertake that work.
So what am I actually paying the expert for?
This is where there can sometimes be confusion. When MAJ Law recommends obtaining an expert report, the additional payment isn't simply another solicitor's fee. It pays for a separate professional to undertake specialist work on your case.
Depending on the circumstances, that work can include:
- reviewing relevant prosecution forensic evidence and documentation;
- considering analytical results and underlying scientific material;
- examining relevant testing or laboratory information;
- identifying matters that require further investigation or clarification;
- applying their specialist knowledge to the evidence;
- preparing an independent expert opinion; and
- where necessary, producing a report compliant with the Criminal Procedure Rules for use in court.
The amount of work required will depend upon the complexity of the case and the type of expert being instructed.
Why does the defence need to pay for an expert?
When you instruct a solicitor privately, your agreed legal fee ordinarily covers the legal work specified within your retainer. An independent expert is a separate professional providing a separate specialist service. Their fees therefore generally need to be paid in addition to your solicitor's legal fees.
At MAJ Law, we appreciate that nobody wants to discover unexpected additional costs during criminal proceedings. If we believe expert evidence is necessary or could be important to your defence, we will explain why it is being recommended and what the expert is being asked to investigate.
The aim isn't to add unnecessary expense to a case. It is to ensure that potentially important technical evidence is properly examined by somebody qualified to do so.
Does paying for an expert mean they will find something wrong?
No - and this is extremely important.
Paying for an expert does not mean you are paying somebody to produce a report that supports your defence. Expert witnesses have an overriding duty to assist the court and must give an objective and unbiased opinion. Sometimes an expert's findings may assist the defence significantly. Sometimes they may identify a narrower issue than initially anticipated. And sometimes their conclusion may be that the prosecution's scientific evidence cannot properly be challenged on the issue they have considered - that does not mean the instruction was pointless.
Until the relevant evidence has been examined by somebody with the necessary expertise, it may simply be impossible to know whether a viable technical challenge exists.
What happens if we don't instruct the expert?
That depends entirely on the case. Not every motoring prosecution requires expert evidence, and MAJ Law would not suggest instructing an expert simply because Part 19 exists.
However, where the defence depends upon challenging a specialist scientific, technical or medical issue, choosing not to obtain expert evidence can mean that your legal team does not have the specialist evidence necessary to advance that particular challenge. This is why your solicitor will explain the reason an expert is being recommended before you decide whether to proceed.
Is a Part 19 expert report the same as a defence?
Not exactly. You may hear people refer informally to a “Part 19 defence”, particularly in motoring cases, but Part 19 itself is not a defence to an offence. It is the part of the Criminal Procedure Rules dealing with expert evidence.
The expert's findings may provide evidence that supports a defence or challenges an important part of the prosecution case, but whether that ultimately provides a viable defence depends on the individual facts and evidence.
Why can expert evidence be so important in drink and drug driving cases?
The prosecution's case may rely heavily upon scientific evidence. For that reason, simply looking at a final number on a laboratory result does not necessarily tell the whole story of how that evidence was produced. Where there is a proper basis for doing so, expert examination allows the defence to investigate the relevant scientific evidence rather than simply accepting the prosecution's conclusion without scrutiny.
The Criminal Procedure Rules also recognise that expert evidence can involve underlying examinations, measurements, tests and experiments. In certain circumstances, another party can require access to records relating to those processes. That can allow an appropriately qualified defence expert to consider the material upon which the prosecution expert's findings and opinion are based.
“I've already paid my solicitor. Why should I pay more?”
We completely understand why clients ask this. The easiest way to think about it is that you are paying two different professionals for two different types of expertise. Your solicitor deals with the law, your case strategy, court procedure, prosecution evidence and your representation. The expert deals with the specialist scientific, medical or technical question they have been instructed to consider. If your case requires both, one cannot necessarily replace the other.
At MAJ Law, if we recommend instructing an expert, we should be able to explain what we want them to investigate, why that issue matters to your case and what their fee covers before you make that decision.
Speak to a specialist motoring solicitor
If you have been charged with drink driving, drug driving or another motoring offence involving technical or scientific evidence, obtaining specialist advice at an early stage can be important.
Not every case requires an expert report. But where expert evidence is necessary, understanding why it is being obtained and what you are paying for can make the process considerably less confusing.
MAJ Law specialises exclusively in motoring and road traffic offences. Our solicitors can review the evidence against you, explain whether expert evidence may be required and guide you through each stage of your case.
Facing a motoring prosecution? Contact MAJ Law to discuss your case with a specialist motoring solicitor.