What is AdBlue?

AdBlue is a fluid used by diesel engines to make their exhaust emissions less harmful. It's actually a marketing name for diesel exhaust fluid created by the VDA, a German auto industry group. The fluid itself is made of deionised water and urea – the same stuff that's in your pee – and, when injected into exhaust, it reacts with harmful nitrogen oxide (NOx) gases, turning them into water and nitrogen.

You won't need to fill up your AdBlue anywhere near as often as regular refuelling – most diesel cars should be able to cover between 6,000 and 7,000 miles on a tank of AdBlue. Refill bottles are available at almost all petrol stations, usually costing less than £15 for 10 litres.