Is an AdBlue Delete Legal in the UK?

Why?

AdBlue feeds the selective catalytic reduction system, which converts harmful nitrogen oxides in diesel exhaust into harmless gases. Modern diesels are type-approved with it fitted and working, so it is part of the emissions control the car is legally required to keep.

Removing the system, or fitting software and an emulator so the car runs without dosing AdBlue, is treated the same way as a DPF or EGR delete: it is illegal to use a vehicle on the road once its emissions control has been altered so it no longer works. The point of a delete is to stop the system operating, which pushes the car's real-world emissions above the legal standard.

It also fails at test time. The MOT and roadside emissions checks are designed to catch exactly this, and the health-and-environment case behind the rules is why enforcement has tightened. Keeping the system healthy is the only road-legal path.