The offence of drug driving was introduced in response to the review of drink and drug driving law by Sir Peter North (the North Report) which found that there was “a significant drug-driving problem”.
Section 5A of the Road Traffic Act 1988 as inserted by s.56 of the Crime & Courts Act 2013 provides that it is an offence for a person to drive or attempt to drive or to be in charge of a motor vehicle on a road or other public place with a specified controlled drug in their body if the proportion of the drug in that person’s blood or urine exceeds the specified limit for that drug.
The offence is drafted in this way because it is not necessary for the prosecution to prove impairment.
THE SPECIFIED LIMITS
The specified limits range from 1 microgram per litre of blood for LSD to 1000 micrograms per litre of blood for temazepam (the Drug Driving (Specified Limits) (England and Wales) Regulations 2014 (SI 2014 No. 2868) as amended by the Drug Driving (Specified Limits) (England and Wales) (Amendment) Regulations 2015 (SI 2015 No. 911). For drugs with medicinal use the limits were set at a level at which there is perceived to be an increased risk of a road traffic collision. For drugs with no medicinal use, the regulations take a zero-tolerance approach. A separate approach is taken to amphetamine in order to balance its medicinal use against its abuse.
It is a defence for D to show that (a) the specified controlled drug had been prescribed or supplied to D for medical or dental purposes; (b) D took the drug in accordance with any directions given by the person by whom the drug was prescribed or supplied and with any accompanying instructions (so far as consistent with any such directions) given by the manufacturer or distributor of the drug; and (c) D’s possession of the drug immediately before taking it was not unlawful under s.5(1) of the Misuse of Drugs Act 1971 (restriction of possession of controlled drugs) because of an exemption in regulations made under s.7 of that Act (authorisation of activities otherwise unlawful under foregoing provisions).
This defence is not available if D’s actions were (a) contrary to any advice given by the person by whom the drug was prescribed or supplied about the amount of time that should elapse between taking the drug and driving a motor vehicle; or (b) contrary to any accompanying instructions about that matter (so far as consistent with any such advice) given by the manufacturer or distributor of the drug. If evidence is adduced that is sufficient to raise an issue with respect to this defence, the court must assume that the defence is satisfied unless the prosecution proves beyond reasonable doubt that it is not.
It is also a defence for D to prove that at the time he is alleged to have committed the offence the circumstances were such that there was no likelihood of him driving the vehicle whilst the proportion of the specified controlled drug in his blood or urine remained likely to exceed the specified limit for that drug (s.5A (3), (4), (5) and (6) of the Road Traffic Act 1988).
The new offence created the need for more laboratory testing of blood and urine samples. Since the abolition of the Forensic Science Service in 2012 testing has been carried out by private contractors. Such contractors must be accredited by the UK Accreditation Service (UKAS). A large number of samples were sent to Randox Testing Services (RTS), who have laboratories in Manchester and Northern Ireland. Accreditation for much of its forensic drug testing (but not alcohol testing) has been suspended. This is because in January 2017 it became known that an operator in the Manchester laboratory had manipulated data relating to quality control testing. It was later discovered that there had been other forms of data manipulation, including the manipulation and fabrication of data during the validation of the methods for analysis of blood and urine specimens for the purpose of s.5A Road Traffic Act 1988.
As a result of this and of the criminal investigation of some employees of RTS, all samples tested by that company will be re-tested by another accredited laboratory. An issue arising from re-testing is the integrity of the samples before their receipt by the new forensic science laboratory. The samples are often in unsealed containers and the conditions of their storage at RTS are not known.
In R –v- Bolton Justices ex parte Scally  QB 537 the Divisional Court quashed the convictions of defendants who had pleaded guilty to driving with excess alcohol when swabs in the blood-sampling kits contained alcohol. In that case, the portion of the sample provided to the defendant was itself contaminated and so the prosecution case could not be properly challenged.
CPS guidance on disclosure in RTS cases states that “investigators, disclosure officers and prosecutors will need to consider every case on its own facts in applying the provisions of the Criminal Procedure & Investigations Act 1996 and the associated Code of Practice”. The Attorney General’s Guidelines on Disclosure (December 2013) provide that in deciding whether material satisfies the disclosure test consideration should be given, amongst other things, to the capacity of the material to have a bearing on scientific or medical evidence in the case (Paragraph 6(d)). Material as to the integrity of samples might reasonably be considered capable of undermining the case for the prosecution or of assisting the case for the accused (s.3(1) Criminal Procedure & Investigations Act 1996). Issues may be raised as to whether such material meets the definition of prosecution material in s.8 (3) and (4) of the Act. It may not be material which is in the prosecutor’s possession and which came into his possession in connection with the case for the prosecution against the accused and it may not be material which he has inspected in pursuance of the Code. It is likely, however, to be material which in pursuance of the Code the prosecutor must, if he asks for the material, be given a copy of it or be allowed to inspect it in connection with the case for the prosecution against the accused.
It is an indication of an advanced system of justice that the courts will intervene when prosecution procedures go wrong. This is particularly important where scientific evidence is compromised (see for example, GMC –v- Meadow  EWCA Civ. 1390).
The position is perhaps best summarised by Dr Richard Gordon in his book The Medical Witness: “Never trust an expert....God knows how many poor folk went to the gallows because of his ignorance and pigheadedness.”
The author is a barrister at Redbourne Chambers.