At present there is no universal device that can quickly determine if a driver has drugs, other than cannabis, in his system. If the police think drugs have been taken the usual practice is to carry out a “Field Impairment Test”. This requires a driver to perform a series of basic tests that might include simple balancing and counting exercises.
If, following these tests, the police have reasonable grounds to believe that you are unfit to drive because of drugs you will be arrested, taken to a police office and required to provide a sample of blood or urine. The same requirement can be made if you are subsequently examined by a doctor who is of the opinion that you are under the influence of drugs. A refusal or failure to provide such a sample is a separate offence of Failing to Provide a Specimen for Analysis.
The requirement for a blood or urine sample can also be made even where the driver has already provided two specimens of breath at a police office which are negative or below the legal limit of alcohol. This might happen if the police initially thought that someone was under the influence of alcohol, rather than drugs or both. If a sample of blood or urine is provided it will be sent to a forensic scientist for analysis to determine if any drug is present. This usually takes a few weeks.