Drink Driving: the ‘hip flask’ defence

Imagine a situation where the police are pursuing a vehicle at high speed, and suspect the driver to be driving whilst he is over the limit (an offence under s5 Road Traffic Act 1988) or whilst he unfit to drive through drink (an offence under s4 Road Traffic Act 1988).  The vehicle comes to a halt, and the driver flees the vehicle and enters his house.  The police give chase.  Before they can apprehend him, the driver manages to consume a whole bottle of whisky.  The police then take a breathalyser reading which reveals the driver to be over the limit.  Blood/urine tests at the police station also show the driver to be over the limit.

It is likely that anyone who has ever watched Traffic Cops on television will have observed a scenario similar to that outlined above.  In such a situation, the defendant is likely to raise the ‘hip flask’ defence.  Contained within section 15(3) of the Road Traffic Offenders Act 1988, this is essentially where a defendant argues that he is not guilty of drink driving because the excess alcohol in his system at the time he took the breathalyser test (or provided a blood or urine sample) was only there because of the alcohol he consumed after he drove the vehicle.  In this article, we will look at what happens when this defence is raised, and how will this affect the defendant at trial.


The Statutory Assumption

As a starting point, under s15(2) Road Traffic Offenders Act 1988, the court will assume that the proportion of alcohol in the defendant’s system at the time of the offence was not less than that shown to be in his system by the relevant breath/blood/urine test.  In the context of the scenario outlined above, this means the court will assume that the breath/blood/urine readings taken by the police are representative of the level of alcohol in the defendant’s system at the time he was driving the vehicle notwithstanding the fact that they were taken after the defendant was seen to consume a large quantity of alcohol.

Additionally, where considerable time has elapsed between the driving of the vehicle and the relevant breath/blood/urine test, it is open to the prosecution to perform a back calculation to estimate the level of alcohol in the defendant’s system, to account for the possibility that the defendant has ‘sobered up’ since he stopped driving.[1]

The ‘Hip Flask’ Defence: s15(3) Road Traffic Offenders Act 1988

However, it is important to emphasise that this statutory assumption is only a starting point.  If the defence can prove that the circumstances in s15(3) Road Traffic Offenders Act 1988 existed, then the defendant will have a complete defence to a charge under sections 3A to 5A of the Road Traffic Act 1988 (which contain all of the main drink driving offences).  In order to avail itself of this defence, the defendant must prove:

(a)    That the defendant consumed alcohol before he provided a specimen of breath/urine/blood for analysis;


(b)   That the alcohol was consumed after the defendant had ceased to drive, attempted to drive or be in charge of a vehicle on a road or other public place;


(c)    That, had the defendant not consumed the alcohol, either:

i.            (If charged with driving over the prescribed limit under s5 RTA 1988) the proportion of alcohol in the specimen provided would not have exceeded the prescribed limit;


ii.            (If charged with driving whilst unfit to drive through drink under s4 RTA 1988) the proportion of alcohol in the specimen provided would not have been such as to impair the defendant’s ability to drive.

(We have briefly considered the distinction between the offences contained in s4 and s5 RTA 1988 elsewhere.[2])

It is absolutely vital to note that it is the defence who must prove that these circumstances exist, and that it must be proven on the balance of probabilities.[3]  The prosecution do not have to prove anything: if the specimen of breath shows that the defendant is over the limit, the s15(2) statutory assumption comes into play with the effect that there is no requirement for the prosecution to prove that the alcohol was consumed prior to the driving taking place.  This means that if the defence are unable to offer evidence to prove that it is more likely than not that the circumstances in s15(3) exist, the court will have no option but to conclude that the defendant is guilty.  This is an important exception to the central criminal law rule of “innocent until proven guilty”.

In order to prove (c) above, in all but the simplest of cases it is necessary to instruct an expert witness to give evidence.[4]  It is very rare (although not entirely unheard of) for the court to accept the defence without a medical expert examining the defendant and concluding that he would have been able to legally drive at the time the offence was alleged to have been committed.  However, if the court considers the defendant to be dishonest (perhaps because he has lied about the amount of alcohol consumed) the court may be entitled to give little weight to any expert evidence tendered on the basis that the expert’s conclusions may have been tainted by the defendant’s dishonesty.[5]

If you are accused of drink driving and wish to advance this defence, we can help you find an expert to provide the evidence required to prove your innocence.

It may also be possible to avoid conviction for other reasons.  One example is the 2013 case of R v M[6], where Mr M was charged with drink driving.  Our barristers noticed that there was a problem with the procedure followed by the police when Mr M took the breathalyser test.  Accordingly, our barristers successfully persuaded the court that this procedural error warranted the dismissal of the case, and so Mr M walked free with his license intact.

Call us for a free consultation if you have been accused of any road traffic offence: our expertise will give you the best possible chance of avoiding a conviction.


The contents of this article should not be relied upon in isolation.  Each case is fact specific and this article should not be treated as legal advice or as a substitute for legal advice.


[1] For example: Gumbley v Cunningham [1988] QB 170

[2] https://www.roadlawbarristers.co.uk/2015/12/drink-driving-what-are-the-limits/

[3] See Drummond [2002] RTR 371 and DPP v Ellery [2005] EWHC 2513 (Admin)

[4] Pugsley v Hunter [1973] RTR 284

[5] R (on the application of Clarke) v Ipswich Crown Court (Unreported) January 1 2013 DC

[6] https://www.roadlawbarristers.co.uk/about-us/case-studies/

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