The effect of S.5(1) of the Road Traffic Act 1988 is to create an offence where a person drives or attempts to drive a motor vehicle, or where a person is in charge of a motor vehicle, after they have consumed so much alcohol that they exceed the prescribed limit for alcohol in their breath, blood or urine.
There is therefore a defence which may be run that the Defendant consumed alcohol after having driven their vehicle, but before being stopped or breathalysed by police.
This is known as the ‘hip flask’ defence, as in the Defendant may have driven their car – soberly or having only consumed a small amount of alcohol – and perhaps experienced an accident, and then decided to consumed alcohol from a ‘hip flask’ afterwards to calm their nerves, only to have the Police arrive and take a specimen from them which shows they had consumed alcohol in excess of the permitted amount, and then be accused of having been over the limit at the time they were driving.
Section 15(2) of the Road Traffic Offenders Act 1988 (“the RTO Act”) creates a presumption that the amount of alcohol measured in a suspect’s sample ‘was not less than’ the amount of alcohol in their system at the time of driving.
This wording prevents a Defendant challenging the analysis as being too high on the ground that because they had only recently consumed alcohol, the alcohol level in their breath, blood, or urine had risen since the time they were stopped by the police.
However, S.15.(3) of the RTO Act allows a Defendant to rebut this presumption with evidence to the effect that the amount of alcohol measured in their sample could only have been achieved by drinking the volume of alcohol claimed to have been consumed after they drove:-
The assumption… shall not be made if the accused proves—
(a) that he consumed alcohol before he provided the specimen or had it taken from him and—
(i) in relation to an offence under section 3A, after the time of the alleged offence, and
(ii) otherwise, after he had ceased to drive, attempt to drive or be in charge of a vehicle on a road or other public place, and
(b) that had he not done so the proportion of alcohol in his breath, blood or urine would not have exceeded the prescribed limit and, if it is alleged that he was unfit to drive through drink, would not have been such as to impair his ability to drive properly.
How do I use the ‘Hip flask’ Defence?
The standard to be met by the Defence is on the balance of probabilities. Depending on the sample evidence and surrounding factors, in rare circumstances it may be apparent on the face of it that the sample level could only have been achieved by the alleged amount of post-driving drinking. If this is ‘obvious to a layman’, this can be a factual defence run without expert evidence (Lord Widgery CJ in Pugsley v Hunter  1 WLR 578).
In most cases though, evidence from a forensic toxicologist is necessary and ought to be sought despite the costs associated with the same.
In DPP vs Singh 1988 RTR 209, an acquittal was set aside on the grounds that the magistrates could not without expert evidence have reliably and confidently concluded that the Defendant had established that the alcohol consumed after driving was sufficient to account for his exceeding the prescribed limit. As a result, the Defendant was held to have failed to discharge the burden of proof.
As confirmed in DPP v Dukolli  EWHC 3097 (Admin), in almost all situations in which a hip flask defence is raised, expert evidence is required. In this case, the Defendant said that he had had a shot of vodka and a bottle of lager before driving, but that after starting to drive he had pulled over to sleep. When the Police came upon him, he averred that he had not drunk any alcohol other than what he consumed before driving, despite having an open bottle of vodka stored on the rear seat. Then, at trial, the Defendant gave evidence which he failed to provide on the night, namely that he had had another mouthful of vodka in the lay-by at that moment that he saw the Police officer approaching. The Defendant did not call any expert evidence and relied on his ipse dixit (his statement without proof).
In his judgment, Mr Justice Openshaw commented at [1.12]:
“In this case, there was a real issue whether the defendant was a credible witness, not least because what he said in court contradicted what he said to the police officer at the time of his arrest, at the time of giving the breath test and indeed in interview. In addition, aspects of his account, such as swallowing a mouthful of vodka as the policeman approached, seemed inherently unlikely. This, in my judgment, is precisely the kind of case where expert evidence is important. Expert evidence would, or certainly may have, enabled the justices to test whether the readings given were consistent with the defendant’s account, and may very well have led to the conclusion that they were not. Furthermore, even if they accepted his story of having a mouthful of vodka, it is not at all obvious to me that a lay person would have found that that mouthful explained or even could have explained the excess.”
The technical analysis required to establish this is sometimes referred to as a ‘back calculation’, to show that the suspect’s alcohol level would have been within the permitted range at the time of driving. Any toxicology report or attempt at back calculation must take into account different factors which vary the effects of alcohol on the individual suspect. For example, a suspect who drinks on an empty stomach will be more intoxicated drinking the same amount of alcohol as a suspect who drank on a fuller stomach.
The report should also address other factors which vary how alcohol consumption affects an individual: the time alcohol was consumed; the weight and size of the suspect; how quickly the alcohol was drank; the type of alcohol, a suspect’s emotional state at the time of drinking; any medication the suspect was on at the time.
What should I expect if I run this defence?
When running this defence, it will naturally be much harder to argue that the Defendant was not in excess of the prescribed limit at the time of driving where the Defendant can be shown to have drank some alcohol before driving, driven some distance, and then continued drinking before a specimen was taken. A lengthier period of consumption is more difficult to back calculate. This defence is generally better run in circumstances where the period of consumption is discrete.
A Defendant running this defence should be prepared that the Prosecution might raise a challenge on the basis that the Defendant is being dishonest in some way about their consumption and the surrounding factors.
The effect of this defence is that the Prosecution is put to proof that the Defendant did not consume alcohol after driving and before the specimen was taken. The Prosecution might do this by challenging the Defendant’s account about how and where they consumed the alcohol, or call witnesses from the scene to the effect that they did not see the Defendant consume any alcohol after exiting their car and before they gave a specimen, if this is available.
The effect of the statutory presumption at S.15(2) above also means that the Prosecution may also call evidence to the effect that while the specimen reading appears low, the Defendant’s alcohol level was in fact higher at the time they were driving. This is more likely to happen in a situation where the specimen was taken a significant period of time after the driving. If this is the Prosecution’s position, it is of course their burden to satisfy the Court of this beyond reasonable doubt, a higher standard than what the Defendant faces in running a hip flask defence.