Being charged with a drink driving offence is not a position anyone wants to find themselves in. However, it is important to remember that the prosecution must prove its case using admissible and reliable evidence.
Understanding the types of evidence commonly relied upon in drink driving cases can help motorists appreciate how these prosecutions are built and why legal advice is often crucial when assessing the strength of the case.
Roadside evidence
Many drink driving investigations begin with a roadside stop. Police officers may stop a vehicle for a variety of reasons, including concerns about a driver’s behaviour, involvement in a collision, or as part of routine traffic enforcement.
At this stage, officers may rely on observations such as:
- The smell of alcohol
- Slurred speech
- Unsteady movement
- Red or glazed eyes
- Admissions made by the driver
- The manner in which the vehicle was being driven
While these observations may contribute to the investigation, they are generally not sufficient on their own to secure a conviction for drink driving.
Breath test evidence
The most common evidence in drink driving cases comes from breath testing. Police may require a driver to provide a roadside breath sample.
If that test indicates alcohol is present or the officer has reasonable suspicion that an offence has been committed, the driver may be arrested and taken to a police station for further testing.
At the station, an evidential breath testing device is used. This equipment provides readings that are intended to determine whether the driver exceeded the legal alcohol limit.
The prosecution will typically rely heavily on the results produced by these evidential machines when presenting their case.
Blood and urine samples
In some circumstances, breath testing may not be possible. For example, a medical condition may prevent a driver from providing a suitable breath sample. Where this occurs, the police may request a blood or urine sample instead.
The prosecution must be able to demonstrate that the sample was obtained lawfully and analysed correctly. Any issues surrounding the collection, handling or testing of the sample may become relevant when the evidence is examined.
Police procedure and documentation
Drink driving prosecutions do not depend solely on alcohol readings. The prosecution must also show that the correct procedures were followed throughout the investigation.
This may include evidence relating to:
- The reason for the initial stop
- The lawfulness of the arrest
- The administration of roadside tests
- The operation of evidential testing equipment
- Custody records
- Officer statements
- Certificates relating to testing devices
If procedural errors occur, they may have an impact on the prosecution’s case.
CCTV, dashcam and witness evidence
Additional evidence can sometimes be used to support a drink driving allegation.
This may include:
- Police body-worn camera footage
- CCTV recordings
- Dashcam footage
- Witness statements
- Evidence relating to a collision or incident
Such material may be used to demonstrate the driver’s condition, behaviour or actions before arrest.
Why the evidence matters
Every drink driving case is different. Although evidential breath, blood or urine results often form the foundation of the prosecution’s case, those results must be supported by proper procedures and reliable evidence.
An experienced drink driving solicitor can review the evidence, identify potential weaknesses and assess whether the prosecution can prove the offence beyond reasonable doubt.