You could check here - some of them are rated, some aren't.
Ultimate Handyman Directory
Also, here is a specific guy with testimonials on his site no mention of sash windows but talented handymen can usually either fix anything or know someone in the trade to recommend:
Handyman in Brighton - handyman in Hove - handyman services : Handyman in Brighton
The other option is to go to a DIY store and ask them if they have recommendations (that's how we found our electrician and hardwood floor installer and both were excellent).
Good luck.