To complicate matters, the A2 was made with two different fuel tanks. Until ~2003, all A2s were fitted with a 34-litre tank. This was changed to a 42-litre tank.
My 2002 TDI therefore has the smaller tank, and I generally get between 420 and 540 miles for each 32-litre fill-up, depending on how the car is used. That equates to roughly 60 to 80mpg. If I had the larger tank, I'd be looking at roughly 720 miles of extra-urban driving.
At the other end of the spectrum, a 1.4 petrol with the smaller tank will have a maximum range of roughly 360 miles of extra-urban driving.
Obviously there are 101 other factors to consider, such as wheel/tyre choice, cruising speed, etc, but this should give you a vague idea.
Cheers,
Tom