Common Police Procedural Errors in Drink Driving Cases
Drink driving investigations follow a strict statutory procedure set out in sections 6 to 11 of the Road Traffic Act 1988 and the associated codes of practice. Every step, from the initial stop through the roadside breath test to the evidential procedure at the police station, must be carried out correctly. Failure to follow the prescribed procedure can render the evidence inadmissible and lead to the case being dismissed.
Procedural errors are more common than many motorists realise. Officers may be inadequately trained, under pressure to process cases quickly, or simply make mistakes. A specialist drink driving solicitor will scrutinise every aspect of the procedure to identify any errors that can be used to challenge the prosecution case.
Even minor procedural irregularities can have significant consequences. The courts have consistently held that the statutory procedure must be followed precisely and that departures from it may lead to the exclusion of evidence. This is why a thorough review of the police paperwork, custody record and device printout is essential in every drink driving case.
Roadside Procedure Failures
Unlawful Stop
Under section 163 of the Road Traffic Act 1988, a police officer in uniform may require a vehicle to stop. However, a requirement to provide a preliminary breath test under section 6 can only be made where the officer reasonably suspects the driver has consumed alcohol, has committed a traffic offence while the vehicle was in motion, or the driver was involved in an accident. If none of these conditions are met, the breath test requirement may be unlawful.
An unlawful stop does not automatically mean the case will be dismissed, but it can form part of a broader challenge to the admissibility of the evidence. If the entire investigation flows from an unlawful stop, a defence solicitor can argue under section 78 of the Police and Criminal Evidence Act 1984 that admitting the evidence would have such an adverse effect on the fairness of the proceedings that it should be excluded.
Incorrect Breath Test Procedure
The roadside preliminary breath test must be carried out using an approved device in accordance with the manufacturer's instructions. The officer must ensure the device is functioning correctly and that the suspect provides a sufficient sample. If the officer uses a device that is not approved, uses it incorrectly, or fails to administer the test properly, the results may be challenged.
The 20-minute observation period is a key procedural requirement. The officer should observe the suspect for at least 20 minutes before the evidential breath test at the station to ensure nothing enters the mouth that could contaminate the sample. Failure to observe this period, or contamination of the sample by vomiting, belching or consuming anything during the observation period, can be grounds for challenging the evidence.
Police Station Errors
Failure to Offer Statutory Option
Under section 8(2) of the Road Traffic Act 1988, if the lower of the two evidential breath readings is 50 micrograms of alcohol per 100 millilitres of breath or below, the police officer must inform the suspect that the specimen of breath will not be used and must offer the option of providing a specimen of blood or urine instead. This is the statutory option and failure to offer it is a fundamental procedural error.
If the statutory option should have been offered but was not, the breath specimen cannot be relied upon by the prosecution. This is an absolute requirement of the statute. A solicitor will check the breath test printout to determine whether the lower reading fell within the statutory option range and whether the custody record confirms the option was properly offered and the suspect's response recorded.
Custody Record Issues
The custody record is a contemporaneous log of everything that happens to a suspect while in police detention. It should record the times of arrival, the administration of rights and entitlements, the provision of legal advice, the breath test procedure and the suspect's responses. Gaps, inconsistencies or missing entries in the custody record can indicate procedural failures.
Defence solicitors routinely request full disclosure of the custody record as part of case preparation. If the record does not show that the correct warnings were given, that the suspect was offered legal advice, or that the testing procedure was completed within a reasonable time, these omissions can be used to challenge the prosecution case.
How Procedural Errors Can Lead to Case Dismissal
The courts have long held that the statutory drink driving procedure must be followed strictly. In the leading case of DPP v Warren [1993], the House of Lords confirmed that the police must comply with the statutory requirements and that failure to do so can render the evidence inadmissible. This principle has been applied consistently in subsequent case law.
Under section 78 of the Police and Criminal Evidence Act 1984, the court has a discretion to exclude evidence if its admission would have an adverse effect on the fairness of the proceedings. Where a procedural error is identified, the defence will invite the court to exercise this discretion. If the court agrees that the error renders the evidence unfair or unreliable, the prosecution case may collapse entirely.
Not every procedural error will result in dismissal. The court will consider the nature and seriousness of the error, whether it could have affected the reliability of the evidence, and whether admitting the evidence would be unfair to the defendant. Serious or fundamental errors are more likely to lead to exclusion than minor or technical irregularities.
What to Check in Your Case
Every drink driving case should be reviewed for procedural errors as a matter of course. Key documents to examine include the MG/DD forms completed by the officer, the custody record, the breath test device printout, the calibration and maintenance logs for the device used, and any body-worn camera footage from the officers involved.
Specific points to check include whether the stop was lawful, whether the roadside test was properly administered, whether the 20-minute observation period was observed, whether the statutory option was offered when required, whether the correct warnings were given, and whether the suspect was offered the opportunity to speak to a solicitor. Any failure in these areas may provide the basis for a successful defence.
Time limits apply to obtaining disclosure of police evidence and device records. Instructing a specialist drink driving solicitor promptly after being charged ensures that all relevant evidence is requested and preserved before it is destroyed or overwritten.