Each station is able to add whatever mark up it chooses as well as change it at any time. Thus a station offering a displayed lower price for standard fuel -4p per litre in my documented example - actually costs MORE because their mark up is enormous. That can change the next time there is a revision of standard prices.
Why should Fuel companies and their franchises be allowed to exploit motorists by subversive pricing this way. To say we have the option not to fill up but driver to another station is no guarantee the next one will be cheaper, nor does it tackle the additional pollution caused by additional starting and stopping, let alone time and fuel wasted. It is fundamentally irresponsible and totally contrary to any claims re Climate Change etc etc. Politicians have not acted on this nor included honesty in their manifestos!