In the UK there are two types of drink driving. The most common is properly called driving with excess alcohol. When you are accused of this you will be made to provide a sample of breath to be analysed by a machine that checks the level of alcohol in your breath. The other type of drink driving is called driving while unfit. You will not be required to give a sample of breath and evidence of your impairment will be provided by police officers describing your behaviour.
The hip flask defence is really intended for the excess alcohol type of drink driving (the one with breath test machine), although in appropriate circumstances you can use it if you have been accused of driving while unfit.
You will need to prove two things to win a drink driving trial using the hip flask defence. The first thing is that you consumed alcohol after driving. The second is that you would have been below the drink driving limit if you had not drunk any alcohol after you finished driving.
You will require two distinct types of evidence to prove each element of the hip flask defence.
The evidence that you drank after ceasing to drive can come from you, in other words, you can get in the witness box at court and tell the judge that you drank after driving. But, if its available, the evidence will be much more effective coming from somebody else.
Proving that you would have been below the drink driving limit is slightly harder. In the vast majority of cases, the court will want to see medical evidence from a doctor who has experience calculating alcohol levels – these are called “back calculations” and are extremely complex. Your own GP is very unlikely to be able to provide the necessary evidence. The only time you won’t require medical evidence is where you had consumed absolutely no alcohol before you drove. Although, it is best to have a witness who can confirm your account!
The hip flask defence usually arises in two situations. First, after an accident where the driver is shaken up and takes a swig from his hip flask (or whatever container he is carrying his booze in) to calm his nerves. The second occurs where police have witnessed what they regard as poor driving but were unable to stop the driver for some reason. At some point later that evening, the police will arrive at the home of the registered keeper and require him or her to provide a sample of breath for analysis. By this time, the driver may have had sufficient to drink that he is over the drink driving limit even where he was stone-cold sober when he got home.
Calling witnesses who can say they were with you before you drove home and you weren’t drinking (or you didn’t drink much) and a witness who can say that when you got home you hit the bottle will increase your chances of success.