Published by Drug Driving Solicitors: specialist defence lawyers for drug driving charges across England and Wales.

7 Things That May Happen After Failing a Roadside Drug Test in the UK

Facing the roadside is stressful enough without having to guess what comes next. If a police officer suspects you of drug driving and asks you to take a screening test, the process that follows is governed by a clear legal framework under the Road Traffic Act 1988 and related legislation. Understanding each stage, what the police can and cannot do, and where you stand at every point, can help you make better decisions and protect your interests.

This article walks through seven things that may happen after a roadside drug test produces a positive result. The stages are not presented in chronological order because the reality of a drug driving investigation is rarely as linear as a flowchart suggests. Different forces handle cases differently, timelines vary, and some stages may overlap or unfold in a different sequence depending on the circumstances. What matters is that you know what each stage involves so that, if it arrives, you are not taken by surprise.

1. The Blood Sample Travels to a Forensic Laboratory

Once a blood specimen has been taken at the custody suite, it does not stay there. The sample is packaged, logged and sent to a forensic laboratory nominated by the relevant police force for independent scientific analysis. This is not a routine health test. It is a legally significant forensic process, and the integrity of the sample at every stage is critical.

Chain of Custody and Why It Matters

The phrase "chain of custody" refers to the documented trail that records who handled the sample, when and under what conditions from the moment it was taken until the analyst receives it. Any unexplained gap or irregularity in that trail can undermine the evidential weight of the result. A specialist solicitor will always examine this documentation carefully.

At the laboratory, analysts test the sample for specific controlled drugs and their metabolites. Each drug has a specified legal limit set by statute. The laboratory report will confirm whether the concentration of any substance found in the blood exceeds the relevant limit. These limits vary considerably between drugs. For example, the limit for delta-9-tetrahydrocannabinol (THC) is 2 micrograms per litre of blood, while the limit for cocaine's primary metabolite, benzoylecgonine, is 50 micrograms per litre.

Crucially, a positive roadside reading does not automatically translate into a positive laboratory result. Roadside screening devices are designed for speed, not precision. False positives do occur. The laboratory analysis is the definitive scientific evidence in any subsequent proceedings, and it is the result in that report, not the roadside reading, that will form the basis of any charge.

2. A Police Officer Issues a Statutory Warning

Before requiring you to provide a sample from a roadside screening device, a constable must first administer what is known as a statutory warning. This is a specific verbal caution required under Section 6(7) of the Road Traffic Act 1988, and it must be given in the prescribed form before the swab or breath test is requested.

The Legal Significance of This Warning

The statutory warning is not a formality. It is a procedural requirement, and if it is not administered correctly, or at all, any evidence gathered as a result may be challenged. Courts have found in favour of defendants where the warning was given in abbreviated or materially different terms to those required by law.

The warning informs you that failure to provide a specimen without a reasonable excuse is an offence. This is important because the law treats refusal as a substantive matter, not merely an act of non-cooperation. Understanding this before you are placed in the position of having to decide whether to comply is one of the reasons early legal advice is so valuable.

In practice, officers administer this warning as a routine part of a stop where drug driving is suspected. It often follows an observation of erratic driving, an accident, or a traffic stop during which the officer notices signs consistent with drug use, such as dilated pupils, slurred speech or an unusual smell. The warning marks the point at which the formal legal process begins, and noting exactly how it was delivered can be significant later.

3. Your Case Is Presented Before a Magistrates' Court

If the decision is made to charge you with a drug driving offence, your case will ordinarily be heard at the Magistrates' Court. Drug driving contrary to Section 5A of the Road Traffic Act 1988 is a summary offence, which means it falls within the jurisdiction of the magistrates rather than the Crown Court, though there are some circumstances in which related offences may be dealt with at a higher level.

What to Expect on Your Court Date

Magistrates' courts hear the vast majority of road traffic offences in England and Wales. The court will be presided over by either a bench of lay magistrates, supported by a legally trained clerk, or by a District Judge sitting alone. The atmosphere is formal, and representation by a solicitor who specialises in this area of law makes a material difference to how your case is presented.

At court, the prosecution will rely on the laboratory report alongside the evidence gathered during the stop and arrest. Your defence will depend on the specific facts of your case. In some instances, the prosecution evidence will be challenged on technical grounds. In others, a statutory medical defence may be relevant. In others still, the focus will be on presenting the court with a full picture of your personal circumstances in order to achieve the most favourable outcome on sentence.

The mandatory minimum sentence for a first drug driving conviction is a 12-month driving disqualification. Courts also have the power to impose a fine, a community order or, in serious cases, a custodial sentence. For professional drivers, those who drive for work, and those with international travel requirements, the consequences of a conviction extend well beyond the courtroom. Preparation, representation and specialist advice are not optional extras at this stage.

4. A Roadside Device Returns a Positive Result

The first tangible indication that you may be facing a drug driving investigation is when the roadside screening device used by the officer produces a positive reading. These devices, known as type-approved drug screening equipment, test a saliva sample for the presence of one or more controlled substances. The most widely used device in England and Wales tests for cannabis and cocaine.

How the Screening Device Works

Type-approved devices work by detecting the presence of a drug above a threshold concentration in saliva. They are designed to be fast and practical in a roadside setting, and they are not the same instrument as the forensic equipment used in a laboratory. The roadside result is, legally speaking, a trigger for further investigation rather than proof of an offence.

A positive result on the device gives the officer reasonable grounds to arrest you and take you to a custody suite. It does not mean you will automatically be charged or convicted. There are several reasons why a roadside positive might not be replicated in the laboratory result, including the sensitivity of the device, the specific drug involved and the time that has elapsed since consumption.

That said, a positive reading marks the point at which the formal investigation begins and the point at which your conduct, what you say, how you behave and what decisions you make, starts to matter in a legal sense. Staying calm, being polite and, as soon as reasonably practicable, seeking specialist legal advice are the most sensible steps you can take at this early stage.

5. You Are Taken Into Custody

Following a positive roadside reading, the officer has the power under Section 6D of the Road Traffic Act 1988 to arrest you and take you to a police station or custody suite. This arrest is not the same as being charged with an offence. It is the mechanism by which the investigation is progressed to the next stage: the provision of a evidential blood sample.

Your Rights at the Custody Suite

On arrival at the custody suite, you will be processed by a custody sergeant who will formally record your arrest, confirm your rights and make decisions about your welfare. You have the right to have someone informed of your arrest and the right to free independent legal advice. That second right is particularly important in a drug driving investigation and should not be waived.

A key right that is sometimes overlooked in the stress of the moment is the right to consult with a solicitor before providing any specimens. The decision of whether and how to cooperate with requests made at the custody suite has direct legal consequences, and those decisions are better made with legal advice to hand. Solicitors who specialise in drug driving are familiar with this process and can provide guidance quickly, often over the telephone.

You will also be asked to confirm whether you have any medical conditions, are taking any prescribed medication or have any reason that might affect the provision of a blood sample. These questions are relevant to the investigation and, depending on your answers, may be significant at a later stage. Answer accurately and retain a record of what you have said.

6. A Decision Is Made to Charge You or Close the Case

Once the laboratory report has been received and reviewed by the investigating officer and the Crown Prosecution Service, a charging decision will be made. This is one of the most consequential moments in the entire process, and it can arrive many months after the original incident.

What "No Further Action" Actually Means

If the laboratory result does not confirm that a controlled drug was present in your blood above the specified limit, or if there are other reasons why the case cannot proceed, you may be told that no further action will be taken. This is commonly abbreviated to NFA. It means the investigation is closed and no charge will follow in respect of that incident.

However, it is worth understanding that NFA is not the same as an acquittal or a finding of innocence. It simply means that the evidence available does not meet the threshold required to charge. In practice, receiving an NFA is a significant relief, but it is also worth asking your solicitor to confirm in writing that the matter is closed.

Where the laboratory result does confirm the presence of a drug above the specified limit, and there are no evidential issues that would prevent the case from proceeding, you are likely to be charged under Section 5A of the Road Traffic Act 1988. The charge will be put to you formally, and you will be given details of your first court appearance. At this point, if you do not already have specialist legal representation in place, securing it without delay is strongly advisable.

7. A Healthcare Professional Collects a Blood Specimen

Once you are at the custody suite, the officer will arrange for a healthcare professional, typically a forensic medical examiner or a registered nurse, to take a blood sample from you. This is the evidential specimen that will be sent for laboratory analysis and, if the result supports a charge, will form the cornerstone of the prosecution's case against you.

Your Entitlement to a Part of the Sample

The process of taking the blood sample is governed by specific procedures set out in the Road Traffic Act 1988. The sample is divided into two parts. One part is retained by the police and sent for laboratory analysis. The other part is offered to you. You are entitled to take your half of the sample and, if you wish, have it independently analysed by a laboratory of your choosing.

This entitlement is not merely a courtesy. It is a right, and the failure of the police to offer you your part of the sample is a procedural error that can have significant consequences for the prosecution's case. If you were not offered your portion, this is something your solicitor will want to know immediately.

The healthcare professional carrying out the procedure is acting in a clinical capacity and is not a police officer. Their role is to take the sample safely and in accordance with the required procedure, not to question you or gather evidence in the conventional sense. You should cooperate with the taking of the sample and raise any genuine medical concerns you have directly with the healthcare professional at the time.

What Happens Next: Taking Control of Your Situation

Failing a roadside drug test sets in motion a legal process that can move quickly in some respects and frustratingly slowly in others. The stages described in this article are not always experienced in a neat sequence, and each one carries its own set of procedural requirements and potential issues. Knowing what to expect at each stage is a significant advantage, and having specialist legal representation in place as early as possible is the single most effective thing you can do to protect your position throughout.

Frequently Asked Questions

What is a DG10 and how long does it stay on my licence?

DG10 is the DVLA offence code assigned to the offence of driving or attempting to drive with a controlled drug above the specified limit under Section 5A of the Road Traffic Act 1988. Once recorded on your driving licence, it remains visible for 11 years from the date of conviction and can be seen by any insurer that checks the DVLA database. The practical effect on insurance premiums can be substantial and long-lasting. A specialist solicitor can advise you on the wider implications of a DG10 for your employment, travel and personal circumstances.

What if the drug found in my blood was prescribed by my doctor?

A statutory medical defence is available under Section 5A(3) of the Road Traffic Act 1988. To rely on it, you must be able to demonstrate that the drug was lawfully prescribed or supplied to you, that you took it in accordance with the advice given by a medical professional, and that your driving was not impaired at the time. The defence exists, but it is narrower in practice than many people assume and must be properly evidenced and formally presented. Drug Driving Solicitors has specific expertise in cases involving prescription medication.

Will a drug driving conviction affect my employment?

For many people, the employment implications of a drug driving conviction are as significant as the court sentence itself. Certain professions, including those involving driving as a core duty, roles in healthcare, law, financial services and positions requiring security clearance, carry explicit obligations to disclose convictions or pending proceedings. A 12-month disqualification can also make it practically impossible to continue in roles where driving is essential. If your employment situation is a particular concern, raise it with your solicitor at the earliest opportunity so that it can be factored into the approach taken to your case.

How long does it take from failing a roadside drug test to being charged?

The process typically takes anywhere from two to six months, although it can take considerably longer. The principal source of delay is the laboratory analysis of the blood sample, which depends on the workload of the force's nominated laboratory. Once the report is returned, the charging decision tends to follow relatively quickly. If six months have passed since the incident and you have not received any communication, specialist legal advice on your position is recommended.

What are the most common reasons drug driving charges are dropped?

The grounds on which charges are most frequently not proceeded with or successfully challenged include: the statutory warning not being administered correctly before the roadside swab was requested; use of a device that was not type-approved for the substance in question; irregularities in the blood sample chain of custody; failure to offer the defendant their part of the blood sample; errors in the laboratory analysis; and an unlawful initial stop and search. A specialist solicitor will examine all of these issues as a matter of course, not only the headline blood test result.

What happens if I decline to provide a blood sample at the custody suite?

Refusing to provide a specimen without a reasonable excuse is a criminal offence in its own right under Section 7A of the Road Traffic Act 1988, and it carries the same penalties as a drug driving conviction, including the mandatory 12-month disqualification. The courts interpret reasonable excuse very narrowly, and any medical reason offered must be supported by evidence. If you are in any doubt about whether you have grounds to refuse, speak to a solicitor before making that decision.

Drug Driving Solicitors is a law firm that focuses exclusively on drug driving cases throughout England and Wales. If you have received a positive roadside drug test result and want to understand where you stand, contact us for a no-obligation initial consultation or visit drugdrivingsolicitors.co.uk. Getting advice early is free and can have a decisive impact on how your case is resolved.