It's not 1p though. Suppose they do this to everyone who buys fuel from them in a day, in a large number of garages? They would be making a fortune from those extra pennies on top of charging us outrageous sums for fuel. It's not the amount of money involved, but the principle.
Funny how oil is now around $50 a barrel but diesel is still £1.11 a litre here - I distinctly recall when oil was last $50 a barrel we were paying well under £1/litre...