Hmm I get around 300 miles from 30 squids in my C12NZ. (oh the joys of 45BHP)
Most of that is crappy town driving stop start **** **** foot to the floor to make the lights, slow down to 30 for speed camera etc etc
So if petrol is 97p a litre.
30/.97 = 30.93 litres. Divide that by 4.5 (roughly no of litres in a gallon) fives me 6.9 gallons.
300/6.9 = 43.5MPG
Not bad I think :D