I would have thought any evaluation would greatly depend on your local neighbourhood average house price of a similar quality to yours.
You should be able to find this out pretty easily, at least it gives you a general figure to work on.
Can't really comment as I've never owned property in the UK, but over here most people these days sell their houses themselves and save an absolute fortune in real estate fees. I personally saved nearly $20,000 in fees when I sold my last house myself. Still need to hire a lawyer to keep everything legal but if it's a simple sale the legal fees are negligible. They give you a kit which includes For Sale signs and all of the paperwork involved, cost me about 300 quid.
This probably doesn't interest anyone in the UK, just thought I'd throw it out there.