As a recent fan of such shows as Murphy’s Law, MI-5, and Life on Mars, I get terms like D.I. thrown at me with reckless abandon. Can someone point to a website (or list, if you have the time) that runs the acronyms, relative ranks, and structure of the main British civil services? Kind of like private > corporal > sergeant > etc. if one were explaining the US military.
The Met, the City of London and a few other forces have a slightly different structure at the top, but basically they have Commissioners and Commanders instead of Chief Constables.
Officers who have the prefix ‘Detective’ before their rank are part of the Criminal Investigations Department (C.I.D.) and are usually plain clothes officers. The rank structure is exactly the same as for uniforms - you get Detective Sergeants (D.S.), Detective Inspectors (D.I.) and so on, all the way up to Detective Chief Superintendents (D.C.S.). A Detective Sergeant, for example, does not outrank his uniformed counterpart.