2.0 HDi economy query

[timdownie]

My 2002 HDiSx Synergie's fuel economy has taken a nose dive. I used to get 38-40 without too much difficulty but recently it dropped to under 30. I've checked my tyre pressures and replaced the air filter and on the last tankfull I recorded 33, still well down on what I used to get. The car's done 33,000 miles. A fair bit of it is short town journeys admittedly but that's not changed.