My old 54 plate st tdci averaged 44 mpg after getting new injectors,filter,service etc.
I thought that was good,what figure are you expecting?
To compare I did the same journey every day to work,used to car share with a guy who had a 2.0 58 plate mondeo hatch,smaller wheels,newer shape,his did 50mpg on the same 50 mile journey and same load (3 people).