If you are facing a charge of drug driving, you should note that blood test evidence is not always flawless.
It is a misconception that you are left with no other option but pleading guilty if you are accused of being over the legal limit.
There are several technical, medical, and procedural defences that can be used to dispute the charge or have the case dismissed. That’s what we’ll focus on in this article, discussing the common grounds for challenging drug driving blood evidence in the UK.
1. Chain of custody & procedure issues
There is a series of standard operating procedures (SOPs) that must be followed; both by police during arrest and sample collection, and along the chain of custody for your sample.
Strict Home Office guidelines and protocols have to be adhered to in police procedure. For example, the Manual of Guidance Drink and Drug Driving (MGDDB) booklet – a mandatory procedural document used by police to legally request and log evidential samples at a police station – must be followed step-by-step.
There must also be continuity along your sample’s chain of custody; that is, the sequence of possession and handling of your sample, from collection right through to its presentation in court. If this chain is broken, or if there are errors during storage or transit to the laboratory, the evidence may be deemed unreliable or inadmissible.
2. Independent blood analysis
You should understand that you have a right to your own blood sample. When police take a blood sample, it must be split into two parts. One part goes to the police lab, and the other should be offered to you.
With your part of the sample, you have the option to have it independently tested. You can send your portion of the sample to a forensic lab for analysis. If their findings do not match the police results or if the levels fall within a lower margin of error, you can use this to challenge the prosecution’s evidence.
Even where independent testing is not carried out, the prosecution is still required to prove that their result is both reliable and accurate.
3. The medical defence prescription drugs
The ‘statutory medical defence’ – under the Drug Driving (Specified Limits) (England and Wales) Regulations 2014 – can be strong grounds to challenge a drug driving charge.
If you are charged with exceeding the legal limit for a specified prescription drug, you may have a statutory defence available to you. The law provides this defence for cases in which the medication was lawfully prescribed to you, and you took it in accordance with medical advice.
You would also typically need to prove that your driving was not impaired, and that you took the medication according to the instructions issued by your pharmacist or doctor.
4. Post-driving consumption
If you can prove that you had consumed drugs after you had finished driving, this might be a valid defence. This scenario demonstrates that you were not under the influence while you were driving, and therefore, the prosecution would not be able to prove a charge of drug driving.
This is known as the ‘hip flask defence’ in drug and drink driving cases, and claims that a driver consumed alcohol after stopping a vehicle (such as after a crash or arriving home), but before a breath, blood, or urine test was given. You should note that this argument requires strong supporting evidence, but has been successfully argued in court.
5. Time-delay fluctuation
Drugs in the blood fluctuate over time. If there was a significant delay between the time you were driving and the time the healthcare professional actually took your blood sample, the result may not accurately reflect your level of impairment or intoxication while you were behind the wheel.
This is a technical argument that may require expert toxicological evidence to demonstrate the fluctuation.
Challenging forensic evidence and police procedure is complex, and it is highly recommended to seek professional counsel from dangerous driving solicitors. You may also wish to refer to information on the Crown Prosecution Service website.