The whole thing was 'decriminalised' so to speak a couple of years ago.
Lets go back to the topic question-
Under no circumstances will you be nicked for wearing a dark visor in bright sunny daylight, no matter how black it is!
Part of the original argument was the fact that legally you could wear as dark a tint sunglasses as you wished, but as far as safety was concerned what happens if you go through a big dark tunnel, a visor can just be lifted bringing back normal vision, whereas sunglasses can't making it dangerous in dark conditions!
Ride at night with a black visor and quite simply you're asking for trouble
Although that never stopped me!