This guide is maintained as a current resource for September 2026 and covers only the laws of England and Wales. Information is for general guidance, not legal advice. Consult a qualified solicitor for advice specific to your situation.
Learn how police investigate drink driving offences in England and Wales, including when drivers can be stopped, how roadside and evidential testing works, what happens if a specimen is refused, and how evidence is used in prosecution. Clear, authoritative guidance for the public and legal learners.
Drink driving is a serious criminal offence in England and Wales. The law is designed to protect everyone who uses the road by deterring and penalising motorists who drive while under the influence of alcohol. Police investigation of these offences follows a structured process set out under the Road Traffic Act 1988 and associated procedures. This article explains how police investigate drink driving, the legal framework, steps taken by officers, and what happens once an offence is under investigation. The aim is to make the law and process clear to members of the public, students, and professionals alike.
1. The Legal Framework
Police investigations into drink driving are rooted in legislation:
- Section 5 Road Traffic Act 1988 makes it an offence to drive, attempt to drive, or be in charge of a vehicle with alcohol levels above the prescribed limits.
- Section 4 RTA 1988 covers driving or being in charge while unfit through drink.
- Section 6 RTA 1988 gives police the power to require preliminary tests.
- Section 7 RTA 1988 allows police to require specimens of breath, blood, or urine for evidential analysis during an investigation.
For prosecuting drink driving, the Crown Prosecution Service (CPS) provides guidance setting out how evidence must be gathered and assessed before charges are brought.
2. When Can Police Stop and Test You?
A police officer may stop a driver and begin an investigation if they have reasonable grounds to suspect:
- the person has been driving, attempted to drive, or was in charge of a vehicle while under the influence of alcohol,
- they have committed a traffic offence while under the influence,
- or been involved in a collision and the officer suspects drink driving.
“Reasonable suspicion” can arise from observable indicators such as erratic driving, the smell of alcohol, bloodshot eyes, slurred speech, or admission of drinking.
3. Preliminary Roadside Tests
Breath Screening
The first stage of the investigation is usually a preliminary breath test at the roadside. This uses an approved screening device. It is important to understand:
- This test indicates whether alcohol is likely to exceed the legal limit; it is not itself evidence used in court.
- You are legally required to comply if the officer reasonably suspects drink driving. Failure to cooperate without reasonable excuse is itself an offence.
- Failing or refusing a preliminary breath test can lead to arrest for further investigation and can carry penalties.
4. Arrest and Evidential Testing
If the preliminary test suggests that the alcohol level may exceed the legal limit, or if the officer has other reasons to believe an offence has occurred, the driver will usually be arrested and taken to a police station or hospital for evidential testing.
Evidential Breath Test
At the station, police will require one or more breath specimens using an approved evidential breathalyser. The device provides data that can be used as evidence in court:
- Two specimens are normally required, and the lower result is used.
- The prescribed limit for breath is 35 micrograms of alcohol per 100 millilitres of breath, though prosecutions typically use a level of 40 micrograms or above in practice.
Blood and Urine Tests
If the breath test cannot be completed (for example, due to injury, medical condition, or unreliable readings), police can request a blood or urine specimen for laboratory analysis.
5. Failure to Provide Evidence
Refusing or failing to provide a required specimen (breath, blood, or urine) without a reasonable excuse is a criminal offence under Sections 6 and 7 of the Road Traffic Act 1988.
Consequences of Refusal
- Failure to provide a roadside breath test can lead to penalty points and fines.
- Failure to provide an evidential specimen at the station can lead to significant penalties, including a minimum 12‑month driving disqualification, an unlimited fine, and potential imprisonment.
Courts often treat refusal to provide a sample as equivalent to a high‑range drink driving offence because the actual level of alcohol in the body is unknown.
6. How Evidence is Used in Prosecution
Once evidential tests are completed, police will prepare a case file for the CPS, including:
- results of breath, blood, or urine analysis,
- officer observations,
- witness statements (if applicable),
- documentation showing proper procedure was followed.
The CPS assesses whether there is a realistic prospect of conviction and if prosecution is in the public interest before issuing charges.
7. Rights of the Person Being Investigated
During the investigation, a suspect has the following rights:
- to be informed clearly of why they are being required to provide tests,
- to be cautioned before evidential testing,
- to consult a solicitor, though time limits may apply,
- to have medical concerns taken into account (with medical evidence) if it affects the ability to provide a specimen.
Police must follow strict procedural rules when administering tests. Errors in procedure can affect the admissibility of evidence in court.
8. Summary of the Process
- Stop and reasonable suspicion: An officer stops a driver on suspicion of drink driving.
- Preliminary roadside test: Screening breathalyser test conducted; refusal or failure can itself be an offence.
- Arrest: If there are reasonable grounds, the driver is arrested for further investigation.
- Evidential testing: Breath, blood, or urine specimens are taken for evidential analysis.
- Preparation for Prosecution: Evidence is reviewed and a decision made on whether to charge.
- Prosecution: Charges are brought in an appropriate court where evidence is presented.
This structure ensures investigations are lawful, evidence is reliable, and defendants' rights are respected throughout the process.
Conclusion
Police investigation of drink driving offences in England and Wales is governed by clear statutory powers and procedural requirements under the Road Traffic Act 1988. Officers use preliminary and evidential testing to determine whether someone has exceeded the legal alcohol limit or is unfit to drive. Compliance with testing is a legal requirement, and refusal carries serious penalties. Evidence gathered during the investigation underpins any prosecution in court. Understanding this process helps road users appreciate how drink driving is detected, investigated, and prosecuted, and underscores the importance of complying with the law for public safety.
