Individuals are more likely to want to commit espionage for another state if they were born in or are a citizen of that state.
Individuals are more likely to want to commit espionage when they are tempted with sex. Why not demand evidence of membership in closed religious communities to address that?
On the latter, because lol that is not going to have the effect you're looking for.
On the latter, you're getting closer to the point I'm making.
And that's how you get numbered groups like the Cambridge Five