I agree with petesims. My sons new Polo TDi is doing similar to yours but now its got over 2k on it, its gradually getting better. He and I thought there was something wrong but when I checked my new Touran TDi mpg against my old one, it was well down. Just as I've hit 2k in it, its gradually improving too. Can almost get 500 miles out of a tank now as opposed to under 400. My old Touran had 17k and I'd get nearly 700 miles from a tank so bear with it.