Hi,
I don't think there's any reliable data to show an area is 'good for writers' unfortunately. Other industry sectors do have more reliable data - Cambridge is hot for technology for instance. When it comes to the more 'Artistic' side of things, then I'd cautiously suggest that all over the UK is where you'll find writers, poets, artists etc etc - there's no real one 'area' for them.
I guess there's perhaps some more suggestions that a particular area of the UK is more suited to 'writers', perhaps see if you can find such information through any relevant websites etc?
Cheers, DtM! West London & Slough UK!