I nominate my favourite Britfilm The Dark Man. The plot itself is easy to follow and enjoyable and Max's motivations are logical to begin with. You can fully understand why he continues in his task throughout most of the film, but when you get to the final quarter he does something that totally negates what he has been trying to do up to that point. It does make for a very exciting finale though.
ps - The Vicious Circle is a favourite of mine too!