John Gaffney is a Detective Chief Superintendent with Special Branch.
Harry Tipper is a Detective Chief Inspector with Scotland Yard.
Tipper works for the Metropolitan Police in the first recorded adventure and quite happy there and certainly fully expecting to stay there for the rest of his career. The activity that makes up that case will bring him to the attention of Gaffney and since the two worked so well together in that matter, they parted company on very good terms.
When a short time later the next case came along for Gaffney, he was in a position of sniffing out a probable bad apple in MI-5 and that called for an experienced man who knew London well, could follow a suspect without being spotted, and was smart enough to notice when subtle things happened that might end up meaning something. Moreover, since the suspect was experienced himself, he would be already quite familiar with every such person at Special Branch. It was at that point that Gaffney remembered the highly intelligent and seasoned Tipper and requested to 'borrow' him for a time. Everyone knew, of course, that if the matter was resolved properly, the borrowing would be in name only and Tipper would have a new home.
Gaffney is the older of the two by likely a decade. He is in his mid-forties and "had been in charge of the Special Branch international squad since his promotion some two years previously". He has been divorced for a small amount of time and does not seem to spend any real time considering it.
Tipper does not appear to be married but we learn very little about his life outside of work leaving us to wonder how much of a life he has there. Certainly to have earned his rank he would have had to be dedicated and there can be no doubt following his actions that he does indeed enjoy his work a great deal.