How much?

Needed to top with fuel, found a Tesco near St Austell. Played the usual game of seeing if you can stop the pump dead on the amount you want to pay, in this case £50. I was too previous but stopped it dead on 50 at the 3rd attempt. Went inside to pay. That'll be £67:95 please. How come? I thought I stopped it dead on 50.00. No, it's definitely £67:95. I was at pump number 3! Have you got the right pump? Yes, pump number 3, £67:95 for exactly 50 litres of fuel! I paid, collected my tesco clubcard points and walked back to the car glad that I was on holiday, unknown and unlikely to be returning to this garage ever again!