A roadside swab that comes back positive or a laboratory result showing a reading "over the limit" can make a prosecution seem inevitable. However, drug driving cases depend on several forensic and procedural stages being handled correctly. Those stages include the roadside test, collection of the blood sample, laboratory examination, and proper disclosure of the evidence to the defence. If a serious problem arises at any point, the prosecution may fail before a verdict is ever reached.
Drug Driving Solicitors has acted for clients in dozens of drug driving matters that concluded with 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 fail.
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 a positive result appears on the device, where a genuine positive is shown by two red lines. The officer's statement also contained inconsistencies about which drug the test had allegedly detected. During cross-examination at trial, those contradictions became clear, and the prosecution accepted that it could no longer establish that the roadside test had actually been positive. That, in turn, undermined the legal basis for requiring a blood specimen. No further evidence was then offered.
Why it matters: roadside testing and the police evidence recording those results are open to challenge in the same way as other evidence. Even apparently minor inconsistencies in an officer's account can become significant enough to undermine the prosecution.
Mr H arranged for part of his own blood specimen to be examined by an independent forensic toxicologist. The expert found that the quantity of blood available was insufficient for a valid analysis. After this conclusion was raised with the Crown Prosecution Service together with a formal defence statement, the prosecution discontinued the case approximately one week before the trial.
Why it matters: strict requirements apply to the amount, handling, and division of blood specimens. Independent analysis of the defendant's portion can identify defects that may not have been raised by the prosecution laboratory.
A number of the firm's cases involved the same important issue: the laboratory responsible for analysing 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 matter, the problem was only identified after the prosecution served its own analytical data pack and the material was examined. Once it became clear that the required accreditation had been lost, the reliability of the analysis was called into question. On the trial date, the prosecution requested an adjournment, but the court refused. No evidence was subsequently offered.
Why it matters: an "above the limit" reading depends on the reliability of the laboratory responsible for producing it. If the laboratory did not hold the necessary accreditation for the test, the result may not withstand scrutiny in court.
Mr Franklin faced a charge of failing to provide a specimen after informing the police that he had a needle phobia. Where a person identifies a possible medical reason for being unable to provide a sample, a medical professional is supposed to determine whether that condition amounts to a reasonable excuse. In this case, however, 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. In light of that evidence and the procedural omission, the prosecution discontinued the case before trial.
Why it matters: a charge of "failure to provide" does not automatically amount to an offence. Where a genuine medical explanation exists, it should be properly assessed. A failure to obtain that assessment can significantly weaken the prosecution.
After Mr Sharpe pleaded not guilty, the court imposed a timetable requiring the prosecution to provide its forensic report and the material underlying it. That deadline was missed. Further directions were issued at another hearing, but those deadlines were also not met. By the time the case returned for a preliminary hearing only a few weeks before trial, the prosecution had still failed to comply. Rather than continue without the necessary evidence being properly disclosed, the case was discontinued.
Why it matters: the Criminal Procedure Rules require the prosecution to provide evidence within the required timetable. Repeated failures to comply are not merely procedural inconveniences. Courts may prevent the prosecution from relying on evidence served too late, which can leave the case unable to proceed.
Mr Singh's case involved an unusual set of circumstances because his blood specimen showed a level below the legal limit. Despite that result, he was charged with the separate offence of driving while unfit through drugs, with the allegation relying in part on statements he had made during a police interview months afterward. Professor Atholl Johnston was instructed as an expert and concluded that the amount detected in Mr Singh's blood did not correspond with what he had described taking and was unlikely to have significantly affected him. Together with a separate error in the hospital's paperwork, that expert evidence contributed to the prosecution's decision to discontinue the case.
Why it matters: the fact that a person has been charged does not establish that the evidence supports the allegation. A result below the legal limit, combined with expert analysis of whether the detected level could realistically have impaired driving, may expose weaknesses in the prosecution's case.
These six prosecutions did not end simply because the police reconsidered their position. Each outcome resulted from an identifiable evidential or procedural problem: unreliable roadside test evidence, an inadequate blood sample, loss of laboratory accreditation, failure to assess a medical explanation, repeated disclosure failures, or a toxicology result that did not support the charge. In every example, the issue had to be identified and supported by a defence team that understood which parts of the evidence required closer examination.
For anyone facing a drug driving allegation, the circumstances surrounding the stop, the collection and testing of the specimen, and the evidence relied upon by the prosecution can be more important than the headline figure shown on a laboratory report. Obtaining advice from a specialist solicitor at an early stage can help determine whether similar evidential or procedural problems may affect the case.
This information is provided for general purposes only and should not be treated as legal advice. The outcome of every case depends on its individual facts.
