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Drink Driving

Drink Drive is not Always a Foregone Conclusion

May 28, 2014

Many people have come to the conclusion that if you are prosecuted for drink driving then you must have been driving over the limit for alcohol and therefore will be subject to a disqualification from driving for at least a year.

In our experience, the numbers of drink drive cases where the prosecution use unreliable readings are on the increase.

The wrong sample!

The client was stopped by police close to where he had been drinking and felt sure that he had not had too much to drink. The road side breath test was conducted by police who would appear to have ignored the need to wait 20 minutes from the last consumption of alcohol (this allows alcohol in the mouth to evaporate and not to make the reading artificially higher). The client was then taken to the police station nearby where he blew between 40 and 50 on the evidential breath machine (these machines should all by now have software which aborts the test if mouth alcohol is detected).

The police correctly offered the client the chance to replace the breath test with a ‘second option’ sample. We stress that if you are ever in this situation, take the opportunity - you have everything to gain and nothing to lose by doing so. The police officer decided that the second sample would be blood; however, he failed to ask the vital question from the set down procedure: “I have decided that the sample will be one of blood, is there any reason why a sample of blood cannot be taken?” A health care professional attended the police station and was unable to take the clients blood, in this case, simply because he was needle phobic. The police had to then switch to a urine sample.

Urine samples have a problem in that the urine contained in the bladder is by its very nature a mixture reflecting the average of the body alcohol levels since the bladder was last emptied. To ensure that the reading reflects the blood alcohol at the time of driving the procedure provides for the bladder to be emptied as the ‘first sample’ which should then be disregarded. The subject should then be given up to an hour to provide a ‘second sample’.  As urine is normally created at a rate of approximately 3ml a minute; after 20 minutes it should be possible to provide a second sample. It is important to note that this sample need not be very much at all, a few drops is enough as long as it is capable of being divided into two. This is where the police in our case also went wrong. Firstly, they took the ‘first sample’ of urine and they failed to divide it into two. This caused two fatal flaws in the prosecution case, the sample tested by the lab would reflect the average over the period including before the client drank, but also the period after he drank but before he drove. It could not therefore be evidence of the alcohol level in his body at the time of the alleged offence. The second fatal flaw was that as the police did not give the client the opportunity to take half of the sample away for his own independent testing, this in itself would have prevented them using the result of their own analysis as evidence leaving them with no case.

It should be noted that where a subject elects to provide a second option sample, unless he goes on to change his mind, the breath reading must be disregarded and cannot be used in evidence to rectify an error, as above, in the second sample.

The prosecution were forced to drop the case without it even going to a trial.


Pete Dodd

About the author

Pete Dodd

Pete joined Nockolds in 2004 as a Partner within the Family Team. Before joining the firm Pete graduated from Bristol University with a degree in ...

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