I know you are looking for skills courses in the south but frankly I think you will get better instruction if you head up north for the weekend. Basically the terrain is more challenging and hence the instructors game needs to be higher. A lovely weekend up north in the Lakes with cycleactive (ask for Chris or Liam) and you will not regret it.
That aside if South is the requirement then I have had friends trained by Ian Warby who used to run Aston Hill in Aylesbury in the South (just North of London) and rated it. Ian now runs the mtb section of the CTC and manages the skills courses coming out of it. So I don't know who actually does the training but Ian is a skilled guy and if he is running the show there I would push you in the CTC direction as Greg recommends
http://www.ctc.org.uk/DesktopDefault.aspx?TabID=4472