Norman Stanley Fletcher,
The reason why there is no guidence on what you can and can't drink is because its not possible to do with any certainty. Today you could drink X amount and in 2 hours not be over, in a weeks time you could drink the same and find yourself in the poo. Which I think is maybe what you are saying. No Goverment, CAA or Airline is going to give you an amount for guidence, because as soon as someone sticks to it and finds they blow over the magic number what do you think they are going to claim in court?
I don't doubt for one minute that no ones going out with the intent to drink and fly.
I agree with you about having a way of self testing, although I would think that Airlines are going to say its your problem not ours. The other thing with that is that as soon as you turn up for duty you could be(and this hasn't been tested in court yet) be seen to be proforming an ancilary function, in which case you commit the offence. An airline isn't going to want you to do that, as they could be seen as condoning it.
So you have a problem of where to site this descreet self testing idea. To be honest if I was affected by this I would buy a screening machine, cost of that against eliminating the risk seems good value to me.