I haven't experienced brumation much, except last year Redrock (rip) went into a semi brumation starting in mid September and lasted until February. I do know there is a link on the home page to a terriffic updated article about brumation. It will give you an idea what to look for and, a suggestion to get him to a good herp vet (If I remember correctly, Miss T is in england, also and could help you with the name of a good herp vet) and get a checkup complete with a parasite check. This is because the symptoms of illness are the same as the symptoms of brumation. The only difference is that if the dragon is ill or has parasites, they will loose weight, if they are just brumating, the weight loss is non existant, except for a few grams.
I do remember reading that some lower the light times to 10 on and a few have put them into a shoe box until they wake up. I suggest reading that article as it will give you a LOT of information regarding what to do with them and, for instance, to get them up once a week for a soak and to make sure they poop before letting them brumate as they shouldn't brumate with food in their tummy as that can make them sick.