A specimen of blood for analysis, used as an alternative to a specimen of breath in cases involving drunken driving. A police officer may require a specimen of blood if he reasonably believes that he cannot demand a breath specimen for medical reasons, if an approved and reliable device for taking a breath specimen is unavailable or cannot be used, or if the defendant is suspected of being unfit to drive and a doctor believes that his condition is due to a drug. A police officer may also ask for a blood specimen if the suspect is in hospital (subject to the consent of the doctor treating him). A suspect may be asked to give a blood specimen under these conditions even if he has already given a breath specimen.
A blood specimen may only be taken with the defendant's consent and by a medical practitioner, otherwise it cannot be used as evidence in any proceedings (DPP v Jackson  1 AC 406). It must be analysed by a qualified analyst, who must sign a certificate stating how much alcohol he found. The suspect may ask to be given half the specimen for his own analysis, which may be used to contradict the prosecution's evidence; if he has asked for but was not given half of the sample, the other half may not be used in evidence against him. A specimen of urine may sometimes be taken as an alternative to a blood specimen.
In all other respects the law relating to blood specimens is the same as that relating to breath specimens.