Under government pressure to make pump prices transparent, the fuel industry will have to prove in the future that UK drivers are paying a fair price for fuel, the AA said.
In the past month, the average pump price of diesel has fallen 4.99p a litre, from 144.30p in mid May to 139.31 now. But UK diesel costs at least 4p a litre more than in Europe.
More top news
Prince Andrew said rumours of a rift over his daughters' participation as members of the Royal Family contain "no truth".
Mourners donned their masks and capes for a special superhero-themed funeral for a comic book fan who killed himself after being bullied.
Drug dealer who posed for selfies with wads of cash from his crimes is jailed for six years.