All the Four Nations have well-guarded Embassies within Horizon from which their spies and agents operate. This is a clause in the Last Treaty.
Another clause gives the Embassies the right to have Registered Spies in Horizon. The Four Nations insisted upon this: the idea was that the Registered Spies would make sure that Horizon never rose as a power again. However, the Horizon negotiating team (which included a much younger Colonel Zero) managed a real triumph: by exploiting the mutual distrust of the Four Nations, they had each country convinced that the other three were planning to use their Registered Spies to spy on their Embassy's business. Thus the Spies work under heavy restrictions - breaking any restriction is grounds for immediate deportation to the Registered Spy's homeland and permanent exile from Horizon and the other three nations.
The names of all Registered Spies must be recorded and sent to the Mayor's Office and the Four Ambassadors. Registered Spies may not enter government offices or private premises without arranging an appointment at least a week in advance, and must be accompanied by a guide at all times as they conduct their inspections. Registered Spies must wear distinctive, brightly-coloured ribbons to indicate which nation they are a spy for. Furthermore, *whenever* a Registered Spy strikes up a conversation with somebody they have not met before they must read the following speech, which is issued to them on a small card:
"Good morning/afternoon/evening, my name is [name] and I am a registered spy for [nation]. I am on official business for my nation's Embassy, and will share all the details of our conversation I deem relevant to my superiors: be advised! If you find my conduct indiscreet or my manner uncouth, please visit the Embassy of [nation] where the staff will gladly help you complete a complaints form. Similarly, if you find my company pleasant and my conversation stimulating, my colleagues will gladly take your feedback into account! Thank you for your patience during this reading of the statutory disclaimer; we may now converse freely."
How they hate that card.
The upshot of this is that there aren't that many Registered Spies. Those who do exist tend to be used not so much as spies as mouthpieces for the Embassies; whenever the Ambassador of a particular country wants to speak to someone he doesn't have time to fit in his schedule (or doesn't want to be seen talking to) off goes the relevant Spy with his ribbon and his card to do business with the chap in question.
Unregistered Spies have a lot more fun. They do the whole James Bond thing. If they are captured or killed the secretary will disavow any knowledge of their existance. But what a fun existance it is.