As this movie has never been released in any form, this has to be a review-by-distant-memory.
A reluctant assassin (Ian Hendry from Get Carter) is hired to shoot a politician (Frank Windsor). Along the way he has a one-night stand with a young woman (Verna Harvey).
It's not long, it's fairly cinematic and it hasn't been seen in public for near-on 40 years, which is a pity.
Despite an explicit shooting at one point, I recall its mood being sombre (rather than Bourne-style action) but it's oddly affecting and I hope someday that it's rediscovered for a decent release. At which point I'll find if my long-distance memory was up to the job of reviewing it...