I suppose if I said my fabia's dash said I got 64mpg on way home last night, it wouldn't be good eh? Best way I have found to keep mpg high is to use the low down torque, where is little boost. Boost is what causes poor mpg, as it's related to fuel injection. Also, keep car in gear when off throttle on downhills as they use ZERO fuel in that state. Momentum alone keeps the engine alive.
I average around the 500 mile mark from a £45 fill-up of diesel, which is fine for me. A bit above 50mpg in reality.