Halfords have reduced the price of Adblue from £20 to £14 for 10 litres of magic juice that stops your diesel car destroying the planet. Or rather, makes it run properly and pass its MOT.
Yes, there have been cheaper deals. However, unlike a motor factors or truck stop, this is available to everyone and is probably more convenient.
Cheaper still with the usual 10% British Cycling discount and Quidco