If it was a service to Saudi Arabia then this would have made a difference, I can see the bars being locked up at that point. To London it seems a bit early, I think it's nearer to the final hour. The immigration issue is interesting, the Border Force are quite used to seeing people stagger their way into the UK, their only concern on that level is for the person's safety. You can't deny admission to European residents on the basis of their sobriety alone, and I doubt it happens much to anyone else either.