Horatio
The JAR 0.02 limit is not intended to allow a few beers the night before. The figure was decided after allowing for any endogenous alcohol and any instrument error in the breathalyser. It is for these same reasons that the Swedes, who have a zero tolerence policy to drink driving, have a 0.02 limit on the roads.
It would be most unlikely for even the most abstinate person to produce a reading of 0.00.
Airclues