Mar 10 2023

Unreliable breath test

We were contacted by Mr B who had been accused of drink driving. He had provided a breath alcohol reading showing that he had 64 microgrammes of alcohol in 100 ml of breath. We were instructed to obtain and review the evidence, then represent Mr B at his court hearing.

We were able to convince the prosecutor that the breath test readings were unreliable and that he should discontinue the case against our client.

To secure a conviction for drink driving, the prosecutor must prove that at the time Mr B drove his alcohol level exceeded 35mcg of alcohol in 100ml of breath. To do this, they rely on the breath test taken by the police. The breath test machine takes two samples from the suspect, two simulator checks and two blank checks. The blanks are used to ensure there is no alcohol in the machine before it takes readings. The simulator checks confirm that the machine is correctly reading the alcohol injected into the machine. The two simulator checks must be within 15% of the drink driving limit, which is 35mcg. The two breath specimens from the suspect must also be within 15% of each other. The reason for all this is so that the court can be sure the breath testing machine has operated correctly and that its reading is reliable.

When we received the prosecution evidence, we were immediately suspicious. The prosecution had served a witness statement from the police officer who conducted the breath test procedure. This sometimes happens, but it’s rare. What stood out about this statement was the length and detail. A typical statement of this nature will fill a page at most, but this one went on for three pages. It seemed over the top as if somebody was trying to hide information by swamping the reader. We looked for the MGDD/A form. This is the written record of the breath test procedure. The MGGD/A was also odd. It was missing important pages, particularly the page that includes the print out from the breath testing machine.

The print out from the breath test machine is important. It shows everything the machine has done: the blanks, the simulator checks, and the suspect’s breath specimens. It also shows the result of the machines internal diagnostic checks.

Upon re-reading the police officer’s very long witness statement, we noted that it provided the result of both breath specimens. We did the maths. Mr B’s two specimens were more than 15% apart. This means two things. First, the breath testing machine has not operated correctly and its results are unreliable. Secondly, the police officers must have known that the results were unreliable and decided to prosecute Mr B anyway. The police must have known Mr B’s results were not reliable because the breath test machine would have printed a warning at the bottom of the print out, which is presumably why it was missing from the evidence! When we asked Mr B if he had been offered a copy of the print out, he said he was not.

It is disappointing that police officers would charge somebody knowing they could not secure a conviction. But, it highlights the importance of taking legal advice from a solicitor who has experience of drink driving case. A solicitor who lacked expertise in drink driving law would likely not have spotted the suspicious factors in the prosecution evidence. They may not have been aware of the significance of checking the readings were within the acceptable limits without the warning on the print out.

The court dismissed the charge against Mr B and granted him a Costs Order that allows us to claim back his legal fees.

If you have been accused of drink driving and would like to speak to an expert motoring law solicitor. Call us today on 020 8242 4440 or visit our contact page and send us an email.