Being pulled over by the police and asked to provide a breath sample is one of the most intimidating and frightening experiences a driver can face. In that stressful moment, under the flashing blue lights, it is easy to feel powerless and to assume that a conviction is inevitable. However, it is vital to understand that the police must follow a strict, detailed, and technical legal procedure when investigating a drink driving allegation. A failure on their part to follow this procedure correctly can often lead to a successful defence.

Understanding this process is the first step toward protecting your licence and your rights. This guide will break down the procedure step-by-step, from the roadside stop to the evidential test at the police station, highlighting where your rights must be protected and where critical errors can occur. When you are facing an allegation of this gravity, you need a legal team that knows this procedure inside out. At Motoring Defence, our specialist drink driving solicitors meticulously scrutinise every action the police take to ensure your rights were upheld and to build the strongest possible defence.

Step 1: The Roadside Stop and Preliminary Breath Test

The process almost always begins at the side of the road.

The Law: The police have the power to stop any vehicle at random. However, to request that you take a preliminary (roadside) breath test, they must have a reasonable suspicion that you have either consumed alcohol, committed a moving traffic offence, or been involved in an accident.

The Procedure: The officer will use a handheld screening device. This is not the "evidential" test; its purpose is simply to give an indication of whether you may be over the prescribed limit. Failing this test (or failing to provide a sample without a reasonable excuse) will lead to your arrest. The drink driving solicitors at Motoring Defence will always question the initial grounds for the stop and the procedure used for this preliminary test as part of a comprehensive defence strategy.

Step 2: The Arrest and Procedure at the Police Station

Following a failed or refused roadside test, you will be arrested on suspicion of driving with excess alcohol and taken to a designated police station that has an evidential breath-testing machine. At the station, the procedure becomes much more formal and is governed by a detailed manual that officers must follow to the letter. This is the most critical stage of the investigation.

Step 3: The Evidential Breath Test – The Critical Stage

The reading from the large, evidential machine at the station is the one that matters. This is the reading that will be used as evidence against you in court. The entire procedure is, or should be, recorded on CCTV and documented on a form known as the MGDDA (Manual of Guidance Drink and Drug Driving).

The Procedure and Potential Defences: An expert solicitor will focus forensically on this stage. Key steps the police must follow include:

• The Statutory Warning:Before you provide a sample, the officer must give you a specific legal warning, explaining that a failure to provide the sample is a separate offence. Any deviation from the required wording can render the process unlawful.
• Health Questions:The officer must ask if you have any medical conditions, such as asthma, that could affect your ability to provide a sample.
• Observation Period:They should observe you to ensure you do not eat, drink, or do anything that could affect the reading.
• The Two Samples:The machine requires you to provide two separate breath samples. The lower of the two readings is the one that is used as evidence.

Our highly experienced drink driving solicitors will always demand the full disclosure of the MGDDA form and the CCTV footage from the breath test room. We meticulously analyse this evidence for the procedural flaws—such as an incorrect warning or a failure to follow the machine’s operating instructions—that can lead to a full acquittal in court.

Step 4: The Alternative Samples – Blood or Urine

In some specific circumstances, the police may require you to provide a sample of blood or urine instead of breath. This might happen if the breathalyser machine is broken or unavailable, or if you have a documented medical reason (like severe asthma) why you cannot provide a breath sample.

The Procedure and Potential Defences: The legal procedure for taking these samples is even stricter. For a blood sample, it must be taken by a qualified healthcare professional, and your consent is required. Any break in the chain of custody—from taking the sample to its analysis in a lab—can be challenged. The drink driving solicitors at Motoring Defence are experts in the complex scientific and legal case law surrounding these alternative samples.

A conviction for drink driving is not a foregone conclusion. The process is technical, and the police are human—they make mistakes. Your licence, your criminal record, and your reputation are on the line. Do not assume the police have done everything correctly. For an expert analysis of the procedure followed in your case, contact the specialist drink driving solicitors at Motoring Defence immediately.