Whilst not being an expert about owning or running a shop I do feel that I know a thing or two about the service that the majority of bike shops in our region offer, I'd say go for it nick and don't let too many people try to deflate your dream by rubbishing the idea or telling you that its not commercially viable to enter the bike shop industry.
There is money to be made in this sector, but IMO it has to be approached in the right way, as misses has already stated most bikeshops seem to be woefully under financed in the early stages, leading to poor stock levels and a lack of skilled staff.
I am from your neck of the woods too (Trowbridge) although now I live in Hampshire, you've got a great opportunity to open a great specialist shop to cater for the region, there's not much competition in the high end road and MTB scene as you just can't get much advice and expertise in this area at the local halfords or its equivalent.
Do it properly, with the right skilled staff and i'm sure you'll do well.
Good luck, and keep us informed of your progress!