Just off topic slightly, but why do people do that?
You use the same amount of fuel whether you put in £5, £50 or £100 at a time. By only putting £30 at a time in you just spend 3x as long at the pumps as I do. I'd rather not be stood on a cold forecourt for any longer than necessary!
It hurts filling up at £90 a time, but it's only once a week, not every 2 days!
Just how many Yorkshire sheep can you fit inside one exhaust?