Sweeney!

Sweeney! is a movie starring John Thaw, Dennis Waterman, and Barry Foster. Hard-bitten Flying Squad officer Jack Regan gets embroiled in a deadly political plot when an old friend asks him to investigate the death of his girlfriend....
When one of Regan's snouts complains that his girlfriend's recent suicide was murder, the flying squad detective feels compelled to investigate. He uncovers a conspiracy that reaches the heart of the government, and finds himself fitted up, suspended and under the scrutiny of Special Branch.