Unfortunately the law is a blunt instrument. In the context of this the "purchase" of fuel is intended to mean "buying fuel and taking it a way in a can for the purpose of setting light to the neighbours garden shed" whereas in this particular instance it was a case of "giving a cashier the money for the fuel my Dad has purchased". In the society in which we now live there is little or no differentiation between the "letter of the law" and the "spirit of the law" either by the person implementing it or the people enforcing it, i.e. the person on the forecourt cannot make a value judgement for fear of the authorities dropping on them like a ton(ne) of bricks if they are caught.
The authorities seem completely unable to apply a "common-sense filter" to borderline cases with the result that minor infringements are prosecuted to the full strength of the law whilst flagrant breaches seem to be ignored if it is felt it might be a bit of work to make it stick.
End of moan, I feel better now .
Shaun