THE FINAL OPTION AKA WHO DARES WINS (1982)
Summary from Netflix:
Inspired by the 1980 siege of the Iranian embassy in London, this exciting actioner stars Lewis Collins as SAS officer Peter Skellen, who infiltrates a terrorist organization intent on using hostages in the American embassy to further its rhetoric. Skellen, who romances one of the extremists, Frankie (Judy Davis), uses his quick wits and even faster fists to tackle the radicals when they demand that a nuclear bomb be dropped on a submarine base.
I will never forget the first time I saw this film. The last 10 minutes were some of the most exiting I had seen. I distinctly remember wanting to learn how to repel through a skylight with a gun blazing. Great film, great acting and a great story. Enjoy.