In a drink driving prosecution, the entire case against you rests on a single, crucial piece of evidence: a number. This number—the reading from an evidential breathalyser or the result of a blood or urine analysis—can seem like an irrefutable scientific fact. However, this "fact" is the end product of a complex chain of technology, scientific procedure, and forensic analysis, and every link in that chain is a potential point of failure.

A successful defence is often not about arguing the law, but about challenging the science. The best drink driving solicitors are not just legal experts; they are also part-forensic-scientists, possessing a deep and technical understanding of how this evidence is produced and where its weaknesses lie. This guide will take you inside the forensic lab to explore how a case can be won on the science. At Motoring Defence, this deep technical expertise is a cornerstone of our practice.

Forensic Focus 1: Deconstructing the Evidential Breathalyser

The sophisticated breath testing machines used in police stations (such as the Intoxilyzer) are not magic boxes. They are complex scientific instruments that use infrared spectroscopy to measure the level of ethanol in a sample of deep lung air. For their readings to be considered reliable evidence, they must be used and maintained perfectly.

An expert solicitor will investigate several key areas of potential failure:

• Calibration and Maintenance Records: These machines require regular, documented calibration and servicing by a qualified engineer. We will demand the full service history for the specific device used in your case. A machine with a history of faults or a missed calibration can have its reliability called into question.
• Mouth Alcohol Contamination: The machine is designed to measure alcohol from your lungs, not from your mouth. "Mouth alcohol" from recent drinking, the use of mouthwash, certain medications, or even some medical conditions like acid reflux (GERD), can contaminate the sample and produce a falsely high reading. This is why the police must observe you for a period before the test. A failure to do this properly can provide the basis for a strong defence.
• Radio Frequency Interference (RFI): These are sensitive electronic devices. The rooms where they are used should be shielded from RFI, which can be emitted by police radios or mobile phones. An expert can investigate if the testing environment was compromised.

Forensic Focus 2: Challenging the Blood or Urine Analysis 🩸

If the police take a sample of blood or urine instead of breath, the potential for scientific error becomes even greater. The sample must be correctly taken, stored, and analysed in a lab using a process called Gas Chromatography.

Specialist drink driving solicitors will work with independent forensic scientists to challenge this evidence on several grounds:

• The "Chain of Custody": We will scrutinise the entire journey of your sample, from your arm to the lab. Was it sealed correctly? Was it stored at the proper temperature? Was it properly labelled? Any break in this chain of custody can lead to an argument that the sample has been contaminated or is no longer reliable.
• The Risk of Fermentation: Blood is an organic substance. If a sample is not stored correctly or does not contain the right level of preservative, it can begin to ferment. This process naturally creates more alcohol within the sample, which means the final lab result will be higher than the actual alcohol level in your body at the time the sample was taken.
• The Statutory Defence (The "Hip Flask" Defence): In cases where a driver has consumed alcohol after driving but before providing a sample, a defence is possible. This requires our forensic experts to perform a complex "back-calculation" to estimate what the alcohol level would have been at the time of driving.

Your Forensic Legal Team: The Motoring Defence Advantage

To win a drink driving case on the science, you need a legal team that is fluent in the language of forensic analysis. At Motoring Defence, our specialist drink driving solicitors possess this deep, technical understanding.

• We meticulously scrutinise the service histories and procedural records for the breathalyser machines.
• We are experts in identifying and arguing issues of potential contamination and procedural flaws.
• We have established relationships with the UK's leading forensic scientists, whom we can instruct to provide independent, expert reports to challenge the prosecution's scientific evidence.

A Reasonable Doubt Can Be a Scientific One

The prosecution must prove its case against you "beyond a reasonable doubt." In a highly technical case like drink driving, that doubt is very often found in the science. An expert solicitor knows exactly where to look for these scientific weaknesses and how to exploit them to build a winning defence.

Do not assume the scientific evidence against you is infallible. Contact Motoring Defence for a forensic review of your case.