A ruling that cast doubt on hundreds of drink-driving prosecutions has been overturned by the Supreme Court. The five-judge court on Thursday unanimously granted an appeal by the Director of Public Prosecutions against the High Court ruling affecting what lawyers for the director described as a “very large” number of drink-driving prosecutions.Prosecutions across the country were put on hold after the July 2025 decision by Judge Sara Phelan quashing a man’s drink-driving conviction over issues concerning the chain of custody of his blood sample.The appeal concerned legal requirements relating to the custody of blood and urine specimens before their analysis by the Medical Bureau of Road Safety (MBRS).The courts annually deal with up to 7,000 drink-driving prosecutions based on blood or urine specimens.The High Court ruled that because of a break in the chain of custody of a man’s blood specimen taken after his arrest for suspected drink driving, he was entitled to have his conviction and two-year driving ban overturned.The specimen was taken on August 21st, 2022, by a doctor who halved it into two glass bottles before sealing the bottles in separate containers labelled with the man’s name and the date.The doctor sealed both containers before handing them to the arresting garda and completed a certificate, required under section 15 of the Road Traffic Act 2010, relating to the taking and sealing of the specimen.The man retained one container and the garda put the second in a box with the section 15 form before sealing the box and posting it for analysis. The MBRS certified that the specimen contained a concentration of 126ml of alcohol per 100ml of blood, more than twice the legal limit of 50ml of alcohol per 100ml of blood.During the District Court trial, the garda witness did not provide direct evidence about the whereabouts of the container, or who had access to it, before it was posted.In refusing a defence application to dismiss over that failure, the District Court relied on statutory presumptions in the Road Traffic Acts that the completed certificates regarding the sample were proof of the facts stated in them unless the contrary was shown.On appeal, the High Court ruled the statutory presumptions did not extend to covering the chain of custody after the container was sealed. The prosecution was required to provide evidence on storage of the specimen, from sealing to posting, to exclude the possibility of interference with it, Phelan said.In her appeal, the DPP argued she was entitled to rely on the statutory presumptions that the certificates relating to the sample were sufficient evidence of its integrity unless an accused could show otherwise.The “logical follow-on” from the “problematic” High Court judgment was that several witnesses might have to be called to prove evidence of the chain of custody, the director’s senior counsel, Eilis Brennan, with barrister David Staunton, argued.Giving the Supreme Court judgment today, Judge Iseult O’Malley said the results of the analysis of a specimen, rather than the specimen itself, was evidence. The Act makes the analysis certificate evidence of those results.There was no general rule of law requiring proof of a chain of custody for real evidence, she said. A failure to prove a chain of custody relating to the specimen did not render the certificate of analysis inadmissible, she said. The issue was rather the weight to be attached to the certificate if evidence was adduced questioning its reliability.Any interference with the seal of the bottles would have been immediately apparent to the analyst opening it and would have meant it could not have been certified, she said.Under the Act, the forms completed constitute sufficient evidence unless the contrary was shown, she held. The prosecution “is not required to exclude every hypothetical possibility”. The High Court erred in finding that “any” failure to comply strictly with a penal statute results in the failure of the prosecution, she ruled. On those and other grounds, the appeal was dismissed.