Thing, I got a substantial reduction in hours required for my PPL in South Africa on strength of my GPL. Many moons ago, yes, and not the U.K., agreed, but seeing as the old South African system was virtually a blueprint of the old U.K. setup, perhaps there may be some truth to this? Certainly worth looking into, I should think?
I think if you had a silver C many moons ago you could convert to a PPL in a minimum of ten hours. I have a silver C and did a JAR-PPL last year. I was allowed one hour off of the minimum of 45 hours for each ten hours gliding up to a maximum of ten hours off. So if you have 100+ hours P1 gliding you can get 10 hours knocked off the 45hr minimum. Mind you, that was last year, it all might have changed again by now.