No, if the 2 readings could be interpreted as showing the machine was not functioning correctly, ie. >15% difference in the readings, then the readings are inadmissible in court. In that case, the officer in charge will decide whether to request a blood sample (taken by a medical professional) or a urine sample instead. Failure to provide in this case is a totally separate offence.
I would suggest that you either accept the facts and go guilty, or instruct a specialist solicitor who will charge you £1,000's to defend him on the premise of finding a loophole. In 99% of these cases, the solicitor recommends going guilty at the last moment as they have nothing (apart from your £10,000 cheque in their pocket!!!)