Carrie Harris is an agent with British Intelligence.
That statement does not really narrow matters down much but then again, getting a handle on exactly who she works for is a major challenge.
In the first recorded adventure we have with her, she is an operative with "a powerful but secretive group seeking to keep the world's powers in balance". In another instance we are told she was part of "the Joint Special Operations Unit, formed of thirty SO19 Metropolitan Police Officers and staff, seconded from a handful of agencies attached to a wider task force from the National Crime Squad. My team was the point of the spear, jabbing into the rat's nest of organized crime in the south east of England."
But my labeling her employer as British Intelligence comes from the first full-length adventure in which she is being interviewed and debriefed and perhaps psychoanalyzed with the tapes of those discussions being classified as Top Secret Eyes Only. In those we learn that Carrie Harris is also Corra Hughes, or perhaps it rightly is the other way. If you are a bit confused, well, so was I but I was also fascinated.
Harris/Hughes is described as a 19-year-old woman, 5'9", 119 lbs and holding the rank of 2nd Lieutenant in the British military. She is said to be "British White" ethnicity with pale skin and shoulder length strawberry blonde hair; a person in excellent physical condition and whose mental state is ruled by the psychiatrist interviewing her as 'stable'. She graduated from Sandhurst.
One vital piece of information concerning her earlier childhood which plays a major role in her attitudes towards many things as an adult is that she was nearly abducted twice, both by the same man with some time elapsing between the two attempts. This has left her quite wary and on guard almost 24/7.
Another important fact about her, regardless of who she works for, is that she is described as a "borderline sociopath" who was "an intelligent and ruthless killer, with a complete inability to know who not to fall for".