In the USA it was decided, many moons ago, that having different TAs for different airfields was probably too much for thick pilots to understand so they took Mt St Helens (before the earthquake), added 1500 ft plus 10% and so came out with a Transition Altitude of 18000 ft which will work whether you are flying out of Miami or Seattle.
Sadly, it appears that our beloved CAA may think the same is true for us... The TA will slowly be aligned to 6000ft across the whole UK at some point.
Personally I think this is a good idea, so my negative comment to the CAA should be taken very much tounge in cheek.