I reckon it is no more than a PR stunt: crude price has fallen, but rather than permanently reduce the cost of petrol, doing it for just two days allows them to claim they have dropped prices but they are still making extra profit 5 days a week! Sure, if you are canny and your life-style and commuting habits can accommodate filling up on cheap days then you are quids in, but I suspect most people cannot.
Apparently energy prices are going down slightly due to all the recent controversy. I think my workshop is likely to get £20 reduction. Wow, £1,980 as opposed to £2,000, whatever will I do with my new found wealth?!