Codename is the cover term for an agency with British Intelligence.
The official designation for this department is MI-17.
We learn a small but highly interesting amount of information from a promotion for the recorded adventures we have of this group: "It's about a British spy ring based at Cambridge and code-named Portcullis, which consists of the master of a College, his daughter, his hatchet manservant, and an international law lecturer". This blurb also tells us that this team is "very sophisticated and devious, too". The College in question is St. Martyr's Residential Hall.
The headmaster mentioned is Sir Iain Dalzell, a man of considerable experience with both the clandestine and the political worlds having been, from comments made by and about him, an operative himself back in the day as well as having served in the House of Commons and as a cabinet Minister.
Assisting him is his also quite capable and very beautiful and elegant daughter, Diana. While her skills as an operative might seem lacking by the fact that in the first adventure we can follow, she is kidnapped, her actions there and subsequently bear out her talents.
The "hatchet" is the highly intimidating Culliford who works as Sir Iain's manservant as his official employment but who is a trained killer and not at all reluctant to show it.
Rounding out this quartet is practicing attorney Philip West, on record as being a visiting lecturer but really on hand to be sent wherever a capable operative is needed.
It should be noted that though these last two, Culliford and West, are both available to field work, the two are not on the best of terms. West is decidedly upper-class-ish while Culliford is far more brutish and menacing.