Notsofantastic
You refer to 'legislation'. Presumably its a typo and you mean BA rules.
The new act of parliament applies to anyone irrespective of thier service in a company, thats legislation.
If BA have started random tests then its done under employment contract and is nothing to do with law.
As for Pilots/Cabin crew not ever drinking or taking things you can't get at the chemists before they fly....The word that springs to mind means testicals!
I worked as Heathrow as a Policeman for 13 years, they do I can assure you, I have been at Court to see them convicted. I also lived with a cabin crew member, and she certainly went to work when she shouldn't have driven let alone flown. (At that stage there was no legislation on aircrew alcohol limits).