I have an 1995 American car which was imported about 15 years ago and
> has been passing MOT tests with no reversing lights for all that
> time.... because yellow bulbs have been inserted in the clear revering
> lens and re-wired to provide indicators ...is this lack of reversing > lights legal?
Yep. No requirement for them to be fitted, and they're never MOTable, even if they are fitted.