Average around 25mpg in city driving and, because I can't help myself, 30mpg on the motorways.
Today I was stuck at 60mph because of traffic and whether and was getting well over 50mpg for ages, but then it all cleared and I booted it

The trouble with the GTI is I find it too difficult to not floor it given the first opportunity.
Lowest I've had is bout 20mpg but that was some hard driving.