If you’re buying or about to buy a new diesel vehicle, and particularly anything larger than a Golf, you’re likely to come into this sooner or later so it’s worth knowing what it is, and what it does; without it, your car simply won’t work.

Ad Blue is essentially an additive consumable for your vehicle, the purpose of which is to neutralise noxious emissions. It’s derived from urea, and is increasingly prevalent in new diesels, as ever greater focus comes onto the higher level of noxious, as opposed to greenhouse, gases that they emit.

So, you’ll have an Ad Blue tank, and you’ll need to keep it topped up. Thankfully, your car will tell you when you need to top up and you don’t need to go to a dealer to do so – many garages sell it at pump, or you can buy it bottled in Motor stores (where it’s much cheaper).

However, do read the manual; you won’t necessarily have a gauge, and the car will have a specific way of telling you how much to add.

How much you need will depend on how much you drive, and the profile of your driving. Urban, congested or aggressive driving creates more emissions, so you’ll churn through it quicker if that applies to you.