Had 1.8 tdci for over two years now, had at best approx 72.5 mpg on a good long run, 60 mpg on local a roads and 52-54 driving around town. basically its the normal advice, drive steady, dont accelerate and brake sharply, anticipate traffic flow. i personnally inflate my tyres 1 psi above the manual to 35 psi, only use quality shell or bp diesel and change my air filter every 12 months, not 36 months on servicing.
i used to use asda diesel
but economy increased, for town driving, from 43 to about 52.
it also helps if you are married to a Advanced driving instructor, sitting in the passenger seat.