Was slightly worried that my gauge read empty at 120 miles, however, the tank carried on to the 240 mile point without cutting out, so all was fine.
I have the following results with regards to mileage:
1st Tank £22.75 - 240 Miles - Price per mile - 9.5p
2nd Tank* £22.00 - 225 Miles - Price per mile - 9.8p
3rd Tank £25.60 - 273 Miles - Price per mile - 9.4p
4th Tank £26.18 - Not finished yet.
This is compared with a price of 17p per mile on petrol.
The reading for the second tankful was a bit funny because the station I filled up at (suthers star garage at longton), seemed to have a broken pump and after about 35 litres started going really slowly and it took about 7 minutes for the next 5 litres so I gave up at 40 litres. When I asked the girl behind the check out if everything was ok with the gas pump she said "Yeah I think so, noone else has complained; I'll make sure I tell some one about it".
I decided not to bother risking not being able to fill my tank up, so wont go back there!