Brad Willis is a scientist.
He is not an agent despite the fact-sheet above listing an affiliation with MI6.
As we are told very early in the first recorded adventure, "Willis wasn't a spy - not in his estimation, at any rate. He wasn't an agent. The Secret Intelligence Service merely considered him a useful asset." A blurb for it tells us that "Brad Willis is an unlikely investigator, and an even less likely spy. He is a scientist, not a hero, but when it comes to finding technical solutions, there is none better. That's how MI6 uses him; that's how he lands himself in trouble."
With that explanation in mind, Willis does work closely, at times, with an MI6 official named Mike Reilly who "wasn't his handler. Spies had those. No, he was merely a communication point when the SIS needed some freelance work done". Still, whenever Reilly and Willis meet up, it would be safe to say that there was going to be trouble somewhere; either Reilly brings a matter to Willis for investigation or, as we find also happens, Willis contacts Reilly and MI6 with some worrisome observation.
Willis is an interesting fellow to observe in that he is quite happy in his academic settings, especially in his position with the Institute of Astronomy in Cambridge, relatively safe to spend time with his research, but he often did long "to go on trips that would take him from his cozy office and transport him halfway across the world to exotic places with palm trees, white sandy beaches and food that even the most critical aficionado would appreciate". Hence his willingness to answer any call from the government.
Willis is described as having a six-foot frame, "solidly build but by no means heavy" with large hands he kept strong enough to handle a hand gun, something he practiced routinely "for the little sideline he sometimes got involved in" (i.e., MI6). This is smart on his part because when he does get the call, he has already learned that he has no idea where he might be heading next or what kind of trouble might be waiting for it, if not already trying to stop him before he even leaves.