I would like to recommend Eric Jude and Son (Cambridge - aka Arbury Road Garage). They are small but very reasonably priced (e.g. £5 to clean idle control valve, £40 to read fault codes, £100 to replace thermostat housing and thermostat on Ford Focus). The owner is an honest guy and takes his job seriously. I had a problem with the car and had it confirmed at two separate garages before using Eric Jude & Son. His is one of the few garages that doesn't charge extortionate rates for fault code reading, which I believe is the biggest rip-off seen in modern garages. The only drawbacks are that he can't accept credit card payments and that, as he's an older gentleman, he won't do the heavy stuff like clutch replacements. Otherwise great.