That does make sense then. You have to be able to see and avoid as you will most probably pass through class E airspace where you might encounter airplanes that are not in contact with ATC and, in the case of gliders, do not need a transponder either. ATC therefore cannot provide traffic information and of course no separation either, both of which are possible in class C. Class D (also used) would not assure separation either. An up to date map of the airspace structure helps there, which is the norm on the LIDO AFC, dunno about Jepp.