The Lands End Transit Corridor was implemented for the same reasons that many helicopter corridors exist between the mainland, offshore instillations and other instillations, to advise the military that the airspace is regualrly used by civillian helicopters and other aircraft up to a certain level.
It isn't mandatory to fly in, it isn't mandatory for anyone to avoid and there aren't any mandatory levels but usually they are from sea level up to 2000ft amsl, however the MOD do strongly advise their aircraft to avoid it if at all possible.
Flying such routes, keeping in touch with ATC and filing a FPL helps you if things go wrong, if you don't want to, you don't have to, but I can't see why any pilot would decline to do so.
Last edited by goatface; 16th Jun 2009 at 19:34.