Police spotting (junction watch)

There is nothing that they can do about it (other than have a word, maybe).

(Similarly, if you are on a bicycle in front of the white line, there is fuck all a copper can do, unless they saw you cross the white line while the light was red.)

Yep, which allows all sorts of abuse from motorised vehicles. Very easy to exploit this on a motorbike. Though I'd argue that motorcycles should often be allowed in them, particularly in the right-hand side to keep bikes in front of cars after filtering on the right.