What is this?

[Chancer]

Lens is shown in the top photo. It's clear but I haven't pulled it yet to determine the bulb

I need to go to Specsavers

Its the bit with the ribs held on with a single screw?

I was wondering what the screw was for

Now that I can guess the orientation I think that it is an aftermarket or retrofit number plate light.

Did the requirement for number plate lights come in much later than number plates and become part of the Ministry of Transport test?

If so then I think its something made as a result of the new demand like the windscreen washer kits in the late 60's or might have been early 70's.