I agree with most people here; lots of different bits could be taught better. Radio is a particularly difficult one; one school I know of teaches a "listening watch" (en-route) which greatly reduces pilot workload but most others get you to talk to everybody on the map which I don't think is right either.
I think the real problem area is navigation. PPL-style visual navigation is inadequate for much UK flight. Unless you have so many hours you can fly the plane with your eyes shut, it is hard work at best and impossible at worst (e.g. vis below 8k).
Perhaps an interesting approach would be to dig up some of the 90%+ of PPLs who pack it in permanently before the first renewal, and ask them why they packed it in. The flight training industry pretends the reason is money. It is in some cases for sure, but lots of people I have met have said they just did not have the confidence to fly anywhere too far.
Incorporation of GPS in the PPL is the only real solution... controversial as hell.