I remember watching a movie on TV like 6 years ago, and I am tying to find the name of it. I remember it took place in England or somewhere in the UK. It had this British guy who was either a politician or a media mongol ( I think it was a politician) who became possessed by the devil or influenced by the devil and he developed something where he sat in his office and when someone opened the door to his office it pulled a string on a handgun he had in front of him and shot him.

This is a wild guess:
The Final Conflict aka The Omen III: The Final Conflict (1981)

Omen III: The Final Conflict (1981) - IMDb (http://www.imdb.com/title/tt0082377/)

https://www.youtube.com/watch?v=Xo-sKst7fMg


As I recall, the suicide happens to the man so that Damien Thorn can step into that political office on his rise to the presidency.