I agree with everything you say, New Judge.....with the exception of the Statutory defence being difficult to sustain. This is an unusual case where the driver has fallen asleep outside his house. I have often had drivers found asleep on, say, a pub car park with keys in the ignition and even with the engine running. If the 'driver' says he had no intention of driving and was merely trying to stay warm and intended to sleep the drink off then a prosecution is likely to fail. In all probability, he wouldn't be charged. In this case, however, the driver is outside his house. Why was he in the car in the first place? He couldn't Liam to be keeping warm otherwise he would have gone into his house.......It might be difficult to prove an intention to drive as he is already outside his house....so where is he likely to be driving to? You know, and I know, that he drove the car there but, in the absence of any evidence to show he drove there, or an admission from him that he had done so, he cannot be charged with driving whilst over the prescribed limit.
He would, as in all cases of being drunk in charge, be interviewed once he was sober and whether or not he ended up with a charge would very much depend on what he said in interview.