For what they charge you'd be better looking locally for a proper "old" independent garage ask about the little independent has little to make by ripping folk off as they have their reputation to protect and dont have the big £££££ to advertise ...
http://www.boschcarservice.co.uk/what-is.php
These fast fit places are always on the "make" and seldomly do a good job as they are rush rush rush
The GP is getting on in years now so most garages are used to them that said if its the 1.2 /1.4 the engine has been around since the 1980's so most garages know them inside out