6 Drug Driving Cases That Didn't Stick and the Reasons Behind It

A positive roadside swab or a laboratory result showing someone "over the limit" may make a prosecution seem inevitable. However, the outcome is not predetermined. Drug driving cases depend on a sequence of forensic and procedural stages, including the roadside test, collection of the blood sample, laboratory testing, and disclosure of the evidence to the defence. If a significant problem arises at any point in that process, the prosecution may fail 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. The following six examples come from the firm's own case history and show the particular issue that caused each prosecution to fall apart.

1. The Officer's Account of the Roadside Test Was Unreliable R v Lewis, Manchester Magistrates' Court [Case Dismissed, February 2023]

In Mr Lewis's case, the arresting officer stated that the roadside drug test had produced a "blue line" indicating cocaine. That description did not match the way the device actually displays a positive result, which is shown by two red lines. There were also contradictions elsewhere in the officer's evidence about which drug the test had allegedly detected. Cross-examination at trial brought those inconsistencies into focus. The prosecution then accepted that it could no longer establish that the roadside test had been positive, undermining the legal basis on which the blood sample had been required. No further evidence was offered.

Why it matters: both roadside testing and the police evidence documenting it are open to challenge. If an officer gives inconsistent or inaccurate evidence about how the test appeared, even a seemingly minor discrepancy can weaken the prosecution to the point that the case cannot continue.

2. The Blood Sample Was Too Small for Valid Testing R v CH, Bexley Magistrates' Court [Case Discontinued, November 2020]

Mr H arranged for part of his own blood specimen to be examined by an independent forensic toxicologist. The expert reached a clear conclusion: the quantity of blood available was insufficient to conduct a valid analysis. After that evidence was presented to the Crown Prosecution Service together with a formal defence statement, the prosecution discontinued the case approximately a week before trial.

Why it matters: strict requirements apply to the amount, handling, and division of blood specimens. Having the defendant's own portion independently analysed can reveal defects that were not identified by the prosecution's laboratory.

3. A Medical Explanation Was Not Properly Evaluated R v Franklin, Cambridge Magistrates' Court [Case Discontinued, April 2022]

Mr Franklin faced a charge of failing to provide a specimen after informing police that he had a needle phobia. When a person raises a potential medical explanation for being unable to provide a sample, the law requires a medical professional to assess whether that condition amounts to a reasonable excuse. In this case, no medical professional was brought in to carry out that assessment. An expert later reviewed Mr Franklin's medical records, consulted with him, and confirmed that the phobia was genuine. Once confronted with that evidence and the earlier procedural failure, the prosecution discontinued the case before trial.

Why it matters: a charge of "failure to provide" does not automatically result in liability. Where a genuine medical reason is raised, the police must ensure that it is appropriately assessed. Failure to do so can seriously undermine the prosecution.

4. The Prosecution Failed to Meet Its Disclosure Timetable Mr Sharpe [Case Discontinued, October 2018]

After Mr Sharpe pleaded not guilty, the court imposed a timetable requiring the prosecution to provide its forensic report and the supporting material. That deadline passed without compliance. A later hearing resulted in further directions, but those deadlines were also missed. When the matter reached a preliminary hearing only weeks before the scheduled trial, the prosecution had still failed to comply and chose to discontinue rather than proceed with the evidence out of order.

Why it matters: the Criminal Procedure Rules impose genuine disclosure duties on the prosecution. Repeated failure to provide evidence within the required timeframe is not merely procedural housekeeping. Courts have declined to allow late evidence to be relied upon, and that can leave the prosecution without the material needed to prove its case.

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

A number of the firm's cases were affected by the same issue: the laboratory responsible for testing the blood sample had lost its UKAS accreditation for the particular testing required under section 5A of the Road Traffic Act 1988. In Mr T's case, the problem became apparent only after the prosecution served its own analytical data pack and that material was examined. Once the laboratory's loss of accreditation was confirmed, the reliability of the analysis itself was placed in question. On the trial date, the prosecution requested an adjournment, but the court refused it and no evidence was offered.

Why it matters: an "above the limit" reading depends on the reliability of the laboratory responsible for producing it. Where the laboratory lacked the proper accreditation to carry out the relevant analysis, the reported result may not withstand scrutiny in court.

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

Mr Singh's case involved an unusual set of circumstances. His blood specimen produced a result below the legal limit, but he was nevertheless charged with the separate offence of driving while unfit through drugs. The prosecution relied in part on statements he had made during a police interview months later. Professor Atholl Johnston was instructed as an expert and concluded that the concentration identified in the blood was inconsistent with the amount Mr Singh had described taking and was unlikely to have had much effect on him at all. Together with a separate mistake in the hospital's paperwork, that expert evidence contributed to the prosecution ultimately discontinuing the case.

Why it matters: the fact that someone has been charged does not mean the evidence necessarily supports the allegation. A below-limit result, combined with expert analysis of what the detected concentration would realistically mean for driving ability, can undermine a case that initially appears stronger than it is.

The Shared Pattern

These six prosecutions were not abandoned simply because the police "changed their mind." Each case involved an identifiable and demonstrable problem: unreliable officer evidence, an insufficient blood specimen, a medical reason that had not been properly assessed, repeated disclosure failures, an unaccredited laboratory, or a result that did not support the charge being pursued. In every example, the outcome depended on a defence team knowing which part of the evidence or procedure required closer examination.

For anyone facing a drug driving allegation, the circumstances of the stop, the way the sample was obtained and handled, and the evidence supporting the prosecution may be more significant than one figure shown on a laboratory report. Obtaining advice from a specialist solicitor at an early stage provides an opportunity to determine whether similar evidential or procedural issues may affect the case.

This article provides general information only and should not be treated as legal advice. The outcome of every case depends on its individual facts.