Paul Stone is an agent with MI-6.
Was. He would make sure you understood the tense, albeit with a bit of a grin. He was asked to leave after a good number of highly successful years. "Cashiered like a bloody crook" is how he puts it right off in the first recorded adventure. He says it to a man from MI-6, or the Special Operations Directorate of it, who has come to Stone's mother's Lebanese restaurant to ask him to do another little job for them. Which is why Stone was so amused at the whole thing.
His dismissal was not for anything he did at this job. He made no mistake that got him in hot water. He learned nothing that would embarrass anyone. His ouster was due to his love of the racetrack.
That would sound bad to most people, implying that he had a gambling problem, and it definitely did to the Powers That Be. Tens of thousands of pounds each year changed hands and that made his bosses nervous. The interesting thing about it all, though, was that the money mostly moved one way - into Stone's hands, not the other way around. And he proudly pointed out that he had "opened his books" to his nay-sayers showing that he only made a few bets each year and that far more were winners than losers. He was very good at what he did and was well compensated for it. He was no security risk. They saw it differently.
Out of work at still a fairly young age, Stone went into a new line of employment; he worked as a private investigator. Interestingly, though, most of his "cases" involved activity out of the country, taking him to many of the same areas he had visited which with MI-6. He was out of the Office but to them he was not out of the business.
Which is why they came to call for his help.