Hi,
If you already work in an RAF control tower then thats a pretty good starting point!!!! I think you already have one up on everyone else right away!!!!
I was lucky enough to get into the ACC and I must say, it was really helpful, as was the visit to Glasgow Tower. The reason I visited these places was because in an earlier post by Gonzo, he said that when he conducts an interview, he wants to see that you have prepared well....i.e. visiting NATS centres, reading ATC books, knowing about NATS as a company etc etc.
I think you'll be fine with the whole visit thing, might be a good idea to read the book "Air Traffic Control" by Graham Duke, I found it extremely helpful and it put me in good stead for my visits.
Is your interview in Glasgow any time soon?