This is too bizarre... The police found John last night at Ealing Broadway station and he was taken to West Middlesex Hospital. To cut a long story short, some time this morning he simply got up and walked out of the hospital and is therefore missing again! I assume that there just weren't enough staff to keep an eye on him 24/7. The police have said they're now looking for him around the clock, but if he managed to get from Brixton to Ealing, he really could be anywhere.
At least he wasn't in too bad a shape when they first found him and at least he'll have had a decent meal and a good night's sleep. Fingers crossed, he'll be found again soon.