<snip> not to mention mention the issue with passing emission tests if they are done in your area
The OP is in Derbyshire County in England. UK drivers have a very comprehensive road worthiness inspection they must pass to keep driving a given vehicle.
The guide to maintaining roadworthy vehicles cites 50 inspection points including "Parking brake performance (judged in %)," "size of tyres, and are the tyres serviceable," "aim of headlamps," "does the horn work."
Exhaust emissions equipment will be looked at, but I don't remember if they actually test the gasses emitted from the tail pipe.
They even do roadside spot checks or did when I was there.
-Jon