Advice needed RE: Breath Difference

Convicted Driver Insurance


New member
I am after some help ahead of directing someone to take up my case.

The situation is thus:
I have a breathalyser print out result, with the following readings, 45 on the first and 38 on the second. The printout also has the error code at the bottom 'Breath Difference' .
I believe there is a good chance of a back calculation being performed.

From doing some reading ahead of any decision made by the police, I have done some reading. Amongst said reading, I came across and read through thoroughly the MGDD/A form...
Now on this form there is a table that states the following at A29(page 18 of 19) :

"From the printout(s) take the lower breath alcohol result. Find this value in one of the rows marked “Lower”. Now take the value below (in the row marked “Max”) and compare it with the other breath alcohol result from your printout(s). If the other breath alcohol result is greater than the value in the “Max” row the breath alcohol analysis is unreliable"

Now, given the above wording, the lower and max number in my situation is 38 and 45. When i look at the table provided at A29 on MGDD, the max for 38 should be 43. I have checked the math and 45 is a difference of 16.8% from the lower reading of 38, which is of course above the 15% difference allowed in the chart provided.
Based on the wording of the MGDD @ A29, these results are 'unreliable'.

Furthermore, earlier on in the MGDD form in the note section, I believe on page 8 between sections A14 it states the following:

"(vii) Where:

a) a device produces an instrument message of:

Breath difference
Interfering substance
Out of range
Mouth alcohol

b) the two breath specimens are taken from different cycles and a comparison of the readings at A29 reveals a breath difference.

then whilst the EBTI may be operating reliably, a reliable indication of the proportion of alcohol in a person’s breath may not have been obtained, and it will be usual to proceed to a requirement for blood or urine under section 7(3)(bb) RTA. (MG DD/B1a/B2c)"

In regards to the above and specifically part 'b' - what does 'taken from two different cycles' mean?

From the above section, it seems as though my situation is covered under part a - Breath Difference, however I was not asked for and did not provide any blood or urine.

Finally, in Section A15 of the MGDD it states:

a) If 2 reliable breath specimens obtained, record printout details at A16, attach printout at A23 and

b) If unreliable specimen(s) or only one or no specimen obtained, record any printout details at A16, attach any printout at A23, do not serve a copy on the accused, consider the notes at A14
(I was served with the seemingly unreliable results!)

So, after all the info above (apologies for lengthy post!) my question is basically, if the machine in the police station produced a reading with an error(Breath Difference), and no blood, urine and/or alternative breathalyser machine was used to take a reliable sample, is the reading the police took admissable in court?

Really need some clarification whether if I am reading this stuff correctly or not(?) but as I said at the outset, I am looking for representation to take this forward as I would not be confident enough to do so.

One more point actually, I have read(but only in one place and the MGDD forms do not say this anywhere!) that the Breath Difference Table is only used where there are two printouts:

"This table is to be used only where there are two printouts, never where (as here) there was a single printout. The table is not concerned with calibration. Whether the machine is reliable depends on calibration. If the machine is not properly calibrated, then it will not provide a reading"

Is there any definitive answer in regards to the Table at A29 and its use etc; as i have been unable to find anything that backs up the above statement(made by a Dr Mundy in the Danny Cipriani drink driving case from 2015/16).

Thanks in advance for any and all help in regards to this matter.

I have read through the forum extensively and did not anything that covers this specific situation.

Martin Hammond

Good morning.

Obviously you have already done a lot of research so I don't need to explain the legal position to you. If the breath readings are too far apart the sample would usually be unreliable and the case discontinued. Back calculations are possible but in my opinion they would be unlikely because they would be back calculated on a reading that would be unreliable.

As much as I am sure it is frustrating I think you need to just wait to see if they do decide to charge you and if they do you, at the first appearance, this issues need to be raised to see how the Crown intend to get around the point.

I hope that helps.

Kind regards


New member
Hi Martin, thanks for the reply. Would it be possible to give me a call as I have another question i would like some advice on. It is a short question, not like above post! Or is there a number I should call?

Again, thanks for the quick reply Martin.