On the quality of his mates, it shows the benefit of sending him to the small local primary school round the corner, rather than anything more academic.
They have known each other since age 3, have all played in each other's houses, and us parents are friends too.
Anyway he has woken up without so much as a headache! 
Apparently his drunkenness was due to a cider drinking competition with the Very Pretty Girl (benefits of a strict upbringing, eh?) Plus the subequent mixing of rum and vodka.
I stayed up watching him breathe until 2am, at which point he got up, explained to me that he had to find a shirt to wear, went to the loo, spent ages doing up his jeans flies and very exactly doing up his belt, then I pushed him back onto his bed and went to bed myself.
And, as I say, this morning he is free of all adverse effects except for the godalmighty flea in his ear.
Thank you for all your help. I was shocked that I knew so little about how to deal with the drunk.