Yes, it has been discussed, and it comes on every forum ad nauseous.
I repeat the advice I received from one of the country's leading motoring lawyers.
If you are on what can be deemed as a public highway, or a space to which the public have free access (such as a pub carpark) then yes you can be done.
The offense of drinking whilst in charge is a statutory offence, i.e. guilty, incumbent on you proving yourself innocent.
As long as you have the keys to the vehicle or they are in your charge, are in the vehicle and over the limit then you can be done.
However both the police and CPS are aware of the "spirit" of the offence, which is to prevent someone getting around a drink-driving charge by pretending to be "sleeping it off".
In applying the spirit the police initially and following that the CPS will look at the circumstances.
Are you stopping by pre-arranged invite? (Britstop for example).
Have you just recently stopped? (Engine warm, no witnesses to you parking up hours ago, etc)....
Is the vehicle capable of being just started up and driven off? (Seats turned round, bed made up etc all suggest no)....
Are you so inebriated that you are likely to still be over the limit at a reasonable time tomorrow morning?
It is up to the individual to consider their vulnerability and act accordingly. There is no golden answer.
From my position if I have turned up, made arrangements with the pub licensee / farmer / cafe owner / etc to stop overnight, have made my bed, have put the keys out of reach but in a safe place, then I feel quite safe to have a drink responsibly, not so inebriated that I cannot hold a reasonable conversation with a police officer, then I would feel quite confident having my day in court should the need arise.
Should I be wild camping, on a public highway or on private land when I could be asked to move on, don't drink.