Agreed - Garages are businesses, but that doesn't excuse misleading clients by failing to tell them it doesn't include an oil and filter change, then trying to flog them one on top when they have your car. That's just downright dishonest, and Stoneacre ought to be ashamed.
I was referring to the diagnostic check not servicing, I have no idea (unless you have a diesel with DPF and a high oil degradation count) why a service wouldn't include a oil filter?