I have an 04 plate Citroen Relay 2.0 hdi. The Ducato jtd engine is an hdi rebadged.
I get between 22 and 28 MPG all local. On a trip to London 18 months ago - motorway 60MPH - around 40 to 42MPG. I also notice that the fuel comsumption is better using Shell/Esso than when using Supermarket fuel. The same applies to our Xsara hdi and my son's Peugeot Partner hdi van.
Lovely engine, great central locking, and love the electric mirrors and windows - also very comfortable.
Weakness is the heater matrix leaks water inside cab - a poor design seal on regulator. First fix is to drain coolant and replace with new antifreeze/summer coolant, which was Citroen's advise and worked on my previous 1.9d 51 plate Relay with 100k on the clock.
Spruce