There is no doubt that the 'British soil' argument is bogus. The Dutch police can - and do - board aircraft at random and breathalyse pilots. I am sure this is the same in Sweden. We do not have Diplomatic Immunity ... and neither should we. If this was the case, would, say, a Belgian truck full of dying asylum seekers be 'off limits' to the UK police? I think not - and would we be happy if an overseas crew were immune from our own laws?
The two issues of alcohol limits and rights of boarding are seperate - we all expect, and have no problem with, a ramp check by the DGAC in Paris or Nice, and similarly we expect free access by our own inspectors to non- UK aircraft here.
The issue we should be addressing is not the actual limit, but how accurate its measurement is and how fair the forensic legal process is thereafter. I believe it differs hugely from country to country.
I fail to see how we as a professional group can argue against an alcohol limit, but we should address an industry wide standard of due process which is just and has no frontiers.