Hi Richard,
A prosecution under s.5(1)(b) of the Road Traffic Act 1988 - being in charge of a vehicle whilst in excess of the prescribed breath alcohol limit - offers a statutory defence of there being "no likelihood of driving" whilst you remained to be over the limit. If properly prepared, argued and accepted by the presiding Sheriff then you would be found not guilty of the charge.
You will require to plead not guilty in the first instance and, in time, obtain an expert toxicology report to demonstrate when, scientifically, you would have been under the legal limit.
In order to advance your defence competently, it would be advisable for you to be legally represented in this case. Please feel free to contact my firm should you wish to discuss matters further.
Regards,
Michael Lyon