Assassination Game-Themed Movie from 70's

by Ghoulog
(Los Angeles, California, USA)

I saw a movie on TV in the 1970's and it may have taken place in Britain.

A lady and a man are flirting on a city street during the daytime. One of them kills the other but no one does anything about it because it is revealed they were contestants in this 'last man standing' game of assassination.

Thank you for any help you can provide.