6 Drug Driving Cases Thrown Out and Why It Happened

A positive roadside swab or a laboratory finding "over the limit" may give the impression that the outcome has already been determined. That is not necessarily so. A drug driving prosecution relies on a series of forensic and procedural stages, including the roadside test, blood collection, laboratory analysis and disclosure of the evidence to the defence. If one stage in that process fails, the prosecution can fall apart before a verdict is reached.

Drug Driving Solicitors has acted for clients in dozens of drug driving matters that concluded through discontinuance, dismissal or acquittal. Below are six genuine examples from the firm's own case history and the particular reason each prosecution failed.

1. The Medical Explanation Was Not Properly Considered, R v Franklin, Cambridge Magistrates' Court [Case Discontinued, April 2022]

Mr Franklin was charged with failing to provide a specimen after he told police that he had a needle phobia. Once a person raises a possible medical reason for being unable to provide a sample, the law requires a medical professional to assess whether it constitutes a reasonable excuse. No medical professional was asked to carry out that assessment in his case.

An expert report, based on Mr Franklin's medical records and a consultation with him, confirmed that the phobia was genuine. In view of that evidence and its own procedural failing, the prosecution discontinued the case before trial.

Why it matters: "failure to provide" is not automatically an offence. Where there is a genuine medical reason, police must have it properly assessed. A failure to do this can undermine the prosecution's entire case.

2. The Officer's Evidence Did Not Stand Up, R v Lewis, Manchester Magistrates' Court [Case Dismissed, February 2023]

In Mr Lewis's case, the arresting officer's witness statement said that the roadside drug test showed a "blue line" for cocaine. A positive result does not display in that way on the device, as a genuine positive result shows two red lines. The officer's account was also inconsistent elsewhere about the drug for which the test was said to have been positive.

These discrepancies were exposed during cross-examination at trial. The prosecution accepted that it could no longer prove the roadside test had been positive at all. This removed the legal basis for requiring a blood sample in the first place, and no further evidence was offered.

Why it matters: both roadside test results and the officers recording them can be challenged as evidence. Inconsistencies in an officer's description of a test, even where they seem minor, may be enough to unravel the prosecution.

3. The Blood Result Was Below the Limit, R v Singh, Swindon Magistrates' Court [Case Discontinued, December 2022]

Mr Singh's case was unusual because his blood specimen returned a result below the legal limit. Despite this, he was charged with the separate offence of driving while unfit through drugs, based partly on statements he had made in a police interview months later.

Professor Atholl Johnston, instructed as an expert, concluded that the concentration found in Mr Singh's blood did not align with what he had described taking and was unlikely to have affected him significantly. Together with a separate error in the hospital's paperwork, this led the prosecution to discontinue the case.

Why it matters: the fact that someone has been charged does not mean the evidence supports the allegation. A result below the limit, or expert assessment of what a particular level would realistically mean for a person's ability to drive, can defeat a charge resting on weaker ground than first appears.

4. The Laboratory Lost Its Accreditation During Proceedings, R v LT, Llandudno Magistrates' Court (March 2021)

Several cases handled by the firm turned on the same issue: the laboratory that analysed the blood sample had lost its UKAS accreditation to conduct the specific tests required under section 5A of the Road Traffic Act 1988. In Mr T's case, the problem emerged only after the prosecution served and the defence reviewed its own analytical data pack.

Once the loss of accreditation had been established, the reliability of the analysis as a whole was in doubt. On the day of trial, the prosecution applied for an adjournment. The court refused the application and no evidence was offered.

Why it matters: an "above the limit" result is only as reliable as the laboratory that produced it. Where the laboratory was not properly accredited to undertake the test, the figure recorded in the report may not stand up in court.

5. The Prosecution Did Not Meet Its Disclosure Deadlines, Mr Sharpe [Case Discontinued, October 2018]

Mr Sharpe pleaded not guilty, after which the court set a clear timetable for the prosecution to disclose its forensic report and the underlying material. The deadline passed without compliance. Further directions were issued at another hearing, but these too were missed.

By the time the matter came before the court for a preliminary hearing only weeks before trial, the prosecution still had not complied. It discontinued the case rather than proceed without the evidence being in order.

Why it matters: the Criminal Procedure Rules impose genuine obligations on the prosecution to disclose evidence on time. Continued failure is not a mere technical issue. Courts have repeatedly prevented the prosecution from relying on evidence disclosed too late, which can be fatal to the case.

6. There Was Insufficient Blood for a Valid Test, R v CH, Bexley Magistrates' Court [Case Discontinued, November 2020]

Mr H sent part of his own blood specimen to an independent forensic toxicologist. The expert reached a straightforward conclusion: the sample did not contain enough blood to permit a valid analysis.

That conclusion, together with a formal defence statement, was put before the Crown Prosecution Service. The case was then discontinued approximately a week before trial.

Why it matters: strict rules apply to the quantity, handling and division of a blood sample. Independent testing of a person's own portion can identify issues that were never flagged by the prosecution's laboratory.

What Connects These Cases

None of these six cases ended because the police "changed their mind." Each depended on a particular and provable issue: an unaccredited laboratory, missed disclosure deadlines, an inadequate sample, an unassessed medical reason, a result that did not fit the charge or evidence that could not withstand scrutiny. In each matter, the defence team had to know exactly where to investigate.

For a person facing a drug driving charge, the details of the stop, the sample and the evidence underlying the allegation may be much more significant than a single laboratory figure. Seeking advice from a specialist solicitor early provides the best opportunity to establish whether any of these issues may apply to the case.

This article is provided for general information only and does not constitute legal advice. Every case turns on its own facts.