Went on a reccy over lunch to see what was out there.
The local starbucks no longer has wifi (the person I asked said it broke a while back and nobody's bothered fixing it). They're Tmobile though so it'll be Tmobile/BT Openworld only.
Costa coffee supports quite a number of providers..
Surf And Sip, Bozii, iPass, Trustive that I could subscribe to (Bozii is only £10 a month so is a possiblity), GBIO, GoRemote, WeRoam, BitBuzz, Boingo and Fatport that I couldn't subscribe to, either because they don't take individual subscribers or are not UK based.
I had a wander into a few other cafes but none of them were wifi enabled, so that's it for my town.
Looks like wifi is a bust

£10 a month for wifi that's only supported in one overpriced coffee shop just doesn't do it for me. Hurry up with the 3G iphone apple!