Blackstone’s Criminal Practice 2018/Part C Road Traffic Offences/Section C5 Drink-Driving and Drug-Driving Offences/DRIVING, OR BEING IN CHARGE, WITH ALCOHOL CONCENTRATION ABOVE PRESCRIBED LIMIT/Defences
The Statutory ‘Hip-flask’ Defence Section 15(3) of the RTOA 1988 (see C5.41) affords a defence to a charge under the RTA 1988, s. 5, where the defendant claims that the fact that he has alcohol in his body above the prescribed limit is attributable to consumption after the event to an extent that, but for that later consumption of alcohol, evidence from the specimen would not have resulted in an offence being made out. Once the statutory assumption (see C5.48) has to be made, the onus shifts to the defendant to raise the ‘hip-flask’ defence (Patterson v Charlton  RTR 18). The defendant must prove, on the balance of probabilities, not only that the reading was wrong but also that at the relevant time his alcohol level was below the prescribed limit (DPP v Tooze  EWHC 2186 (Admin)). In Drummond  RTR 371, the Court of Appeal decided not to ‘read down’ s. 15(3) under the HRA 1998, s. 3, so that it imposes only an evidential burden (see, e.g., Lambert  2 AC 545 at F3.18) and ruled that the persuasive burden imposed does not interfere with the presumption of innocence in the ECHR, Article 6(2), because it is no greater an interference than is necessary. This approach was confirmed as remaining correct post-Sheldrake (see C5.51) in DPP v Ellery  EWHC 2513 (Admin).
The defence also extends to offences under the RTA 1988, ss. 3A and 4 (see C3.20 and C5.58). In the case of an offence under s. 3A, evidence of post-accident consumption of alcohol is admissible even if the defendant drove after the accident because s. 3A looks at the state of intoxication at the time the cause of death arose. In Dawson v Lunn  RTR 234, Robert Goff LJ said (at p. 238):
…there are circumstances in which, as a matter of common sense, laymen can reach a perfectly sensible conclusion unaided by scientific evidence. We need only to take the simple case of somebody who satisfies the justices on the evidence that he had drunk only a small amount before driving, and that after ceasing to drive he had drunk a substantial quantity of alcohol. The justices can then conclude as laymen, reliably and confidently …that the defendant has satisfied them, on the balance of probabilities, that he has consumed alcohol after ceasing to drive and that had he not done so the proportion of alcohol in his breath, or blood, or urine would not have exceeded the prescribed limit. But there must be cases where the justices cannot sensibly draw that conclusion themselves unaided by expert evidence.
He went on to adopt the passage in Pugsley v Hunter  2 All ER 10 (a case on ‘special reasons’), where Lord Widgery CJ observed that ‘unless the case really is an obvious one …the only way in which a defendant can discharge the onus is by calling medical evidence’. The Court of Appeal also discouraged reliance upon extracts from scientific journals. Except perhaps in the clearest of cases, the defendant must therefore call scientific evidence (DPP v Singh  RTR 209). Where there is no expert evidence, the justices should avoid drawing their own conclusions about the probable effect of the claimed consumption of alcohol (Lonergan v DPP  RTR 188) and must be careful when assessing the credibility of the defendant (DPP v Dukolli  EWHC 3097 (Admin)). Where the justices have the benefit of expert evidence, despite apparent discrepancies, they may be entitled to find that the defendant has discharged the onus on him (DPP v Lowden  RTR 349).
If expert evidence is to be called, it should be disclosed to the prosecution to avoid unnecessary adjournments (DPP v O’Connor  RTR 66).
Other Defences Section 5(2) of the RTA 1988 provides a defence to an allegation of ‘in charge’ of the vehicle, based on the likelihood of the defendant driving while still above the prescribed limit. In Sheldrake v DPP  1 AC 264, the House of Lords determined that there was no need to ‘read down’ this reverse onus of proof as an evidential burden only (as the majority of the Divisional Court had, relying on the presumption of innocence in the ECHR, Article 6(2)) and that this was a provision properly imposing a legal burden on the defendant, which was justified as pursuing a legitimate objective that was neither unreasonable or arbitrary. See F3.18 for a full discussion of the ‘reverse burden’.
It is not sufficient for the defendant to prove that he did not intend to drive. The question is whether he has shown that there is no likelihood of driving while still over the prescribed limit (CPS v Thompson  RTR 70); ‘likelihood’ means real risk (Sheldrake v DPP  QB 487). In Drake v DPP  RTR 411, the Divisional Court held that the presence of a wheel clamp on a motor vehicle could not be disregarded when considering the likelihood of the defendant driving. Medical or other expert evidence will almost inevitably be required to establish the probable alcohol level at the time at which the defendant will next drive (DPP v Frost  RTR 11), unless the length of time involved makes that conclusion obvious. As to duress, see A3.35 to A3.52.
Insanity cannot be raised as a defence as there is no mens rea element to which it can relate (DPP v H  1 WLR 1406, but see A3.24 for criticism about the correctness of this decision).