I have the same issue, averaging around 49 - 52mpg. I drive 500 miles a week , 50mile journey twice a weekday. The car has now done over 7000miles and spent almost 4 weeks off the road with the dealership for investigation into noises, vibrations and poor fuel consumption. (Note that the handbook says fuel consumption will settle down after 1,800miles.)
I raised my concerns with the dealership within the first two weeks of taking delivery of the car in October 11. I have also complained direct to Citroen UK. Only this week I received a letter from Citroen UK stating '
The fuel consumption is within the expected range for regular day to day use and doesn't indicate a problem.'
For me, the principal selling feature of this car was the advertised fuel consumption. The alternatives were BMW 3 series and Ford Focus both rated at 52mpg in 2litre diesel auto. Whilst the Citroen has good looks, if the fuel consumption had not been so significantly greater than 52mpg, the quirky gearbox - which I was told is how the advertised great economy is achieved - is hardly a selling point.
It is interesting to note the quote from Linda Jackson the MD of Citroen UK...'Buying a car is a big commitment and customers need to feel confident.' I did when I bought it, but now I feel conned - and let down by both the dealership and Citroen UK.