essbee - hope you don't mind me posting all this, but know you probably want other opinions on the various assessment/diagnosis venues. I've talked to BIBIC and Elliot House and am going on my knowledge of the dev paed/SALT team.
BIBIC : as Jimjams has mentioned, they don't diagnose (I was wrong when I said they did). They will give a full assessment - ie, this is where he is in this time and place - and also a therapy programme for at home and at school. They also offer reassessment visits to update therapies.
Elliot House : the lady there told me that they mainly deal with autistic spectrum disorders. Usually people have a tentative diagnosis with a local paed or psych and are referred from there. They can diagnose adhd, but it usually happens when a local professional suspected autism, iyswim. It doesn't sound like the place for your son. The woman I talked with was lovely, though, so if anyone else is in the position where autism is suspected, it's worth a call.
The dev paed/ SALT team near you: as you know, I've been through this. They're great and offer a diagnosis. Socci has also been to them. We're two very different cases (in mine: some speech and language difficulties combined with behavioural issues and in hers: autism). I'm not sure what sort of therapy they recommended to her, if any, but in my case, esp with the behavioural stuff, the advice was golden. But they did just recommend getting SALT - nothing specific... of course, that has worked (just getting a good SALT).
Soooo.. if it were me, I'd go to the dev paed/SALT if you want a diagnosis and idea where to go for therapy and BIBIC if you want a plan of action. I'd go for the diagnosis first, if simply to know what it is that's driving him. But that's me and the above info is just what I know from phoning around and info packets (except the dev paed/salt, obv!)
Please, anyone feel free to add to/correct it!