I think, AB, that if you were merely sitting as a passenger in a car the driver of which happened to be drunk, it would, in normal circumstances, be a very difficult prosecution indeed with which to succeed to show that you were “aiding and abetting” an offence of driving with excess alcohol. It would have to be shown that:
(a) You were aware that such an offence was being committed (which would mean you would have to be aware of the level of alcohol present in the driver’s system)
(b) You actively assisted in the commission of the offence (which would mean you had to either assist in the driver’s intoxication and you had to be complicit in forcing him or at least encouraging him to drive)
(c) Both of the above would have to have been carried out intentionally.
Similarly, the suggestion by “DrinkDriving.org” that if you fail to identify the driver, and the Police cannot establish his identity, you can be prosecuted for being "in charge" of the vehicle would be equally difficult with which to succeed. There are certainly circumstances where all occupants of a vehicle decamp following an incident and the police have difficulty identifying the driver, then they will often breathalyse all occupants so that the intoxication of all of them is measured until and unless it can be established which of them was driving. But their suggestion that in such circumstances a passenger could be charged with being over the limit whilst “in charge” of the vehicle is far-fetched.
A passenger has no obligation to identify the driver of a vehicle in which he is travelling (indeed he may not even be aware of that information). Further, sitting as a passenger in a vehicle does not suddenly make one “in charge” if the driver has left the scene or cannot be identified.