Philip Mangan is a reporter.
While he does not work for any particular company as far as I can tell, his beat is the Far East and his home base seems to be Beijing. He has been working as such for quite some time and is very comfortable with his chosen region and his contacts.
Certainly the above is what is believed by the British Intelligence agent who first connects with Mangan while in China. That man reports back to headquarters that Mangan is "freelance, holds a current accreditation and files regularly for a major London title and for a small television news agency.
It is a very good thing he is so at home with it all in the Asian Pacific region because he most definitely stands out wherever he goes in the area, being 6' tall with red hair and green eyes. It would be quite difficult to not spot the man in a crowd in the capital of China or anywhere else in that part of the continent despite his occasional attempts to remain inconspicuous.
Mangan has no desire to get involved with anyone from any intelligence community whether it be Chinese or his native Britain but unfortunately for him, neither of those nations bothered to ask him if he wanted to play. They, and life, just showed up for the game and suddenly Mangan is a popular man.
As a result of things that Mangan inadvertently gets involved with in the first recorded adventure, his connection to the SIS will become more solidified though it is still not something he is happy with. Patterson, the woman who would become his handler, of sorts, explains that she was authorized to offer him "an association" in which he would go "on the books" which she says is not "uncommon" though nowadays less so with journalists.
It is this association that will really get him noticed, something that is never good for one's health.