I have when I lived in Wales. it was quite common to see them stopping & dipping vehicles.
They test for the following chemicals.
- Coumarin a UK marker
- Quinizarin a UK marker
- Solvent Yellow 124, a marker used in all EU Member States.
If they find these chemicals they know you've had Red diesel, Kerosene or other duty exempt fuel. in your fuel system. you see there not testing to see what fuel your running on. They're looking for reduced duty/duty free fuel, in your tanks. If they find any trace your in the ****e.
Your MOT expert doesn't know what he's talking about. Road fuel diesel doesn't have any of these marker chemicals in it. Kerosene does. So how can it be indistinquishable??