Odd one...
5 miles a day would not be enough to allow a DPF regen. When mine has done it the car's fans can run on for 10-15 mins after the switch off. A run down to Tuscany will definitely clean it out though.
It might have had new software put in as part of the service, but nothing obvious I can think of for causing the mpg to fall unless the new air filter (was one fitted?) isn't as 'free flowing' as the previous one, or a hose isn't on properly.
Are your tyre pressures OK? Too low a pressure could do it perhaps..
![Confused :?](./images/smilies/unsure.gif)