Interesing point you raise, Rowardennan.
I'm afraid it says a lot about the society that the police would rather than wait until an offence has been comitted than prevent it!
Having followed the debate, though, I draw the conclusion, by mixing the various sources that one could, if one dared, consume one unit of alcohol whilst on duty and remain below the o.2 promille limit with the blessing of the WHO.
Fortunately , the SOP's state "No alcohol whilst on duty or in uniform!!"