Carl,
Have always had the local motorsave in Lincoln do any fitting and balancing as they're quite cheap IIRC. These are with tyres that I get off of the bay. Alternatively, try
http://www.allnewtyres.co.uk.
that's where all ours have come from. Our back up is Bush tyres in Horncastle as they're always a helpful bunch!
Kwik Fit - Satan's service outlet IMO