My 1.6tdi averages about 40ish mpg most of the time, and probably does about the same as yours on the motorway golfgtipaul. But has only done about 3500 miles so still has to run in a lot. Mpg doesn't really get any better on the motorway either. Have seen photos on here taken by peeps showing really high mpg's on both diesel and petrol cars, but this is easily done, just wait till the engine has warmed up and press the reset button on the underside of the rhs stalk. Could have easily posted a pic of my dash with 80ish mpg on the other day.
Night Flight, is your daily commute really short ie a couple of miles? As these engines seem to take ages to warm up, and assuming that your mpg is so low your car must be permanently cold and doing a regen on the dpf, indicated by a tickover of 1000rpm plus, and a slight smell of burning in the car for good measure.
Hate to agree with dealers comments but seriously wait till 10000 miles to see results, have posted before on here about my last
ibiza which was a 100hp formula sport, which liked its fuel to begin with, but when I swapped it I could easily get 45 - 50mpg out of the thing.