Not exactly helpful, since neither difficulty level nor government affect the chance of successful infiltration. The only way of expelling an enemy spy is placing on of your own in the city; and if the enemy spy is good even this may not work.
Also, there IIRC is a bug that will cause the gates to be permanently open even after the spy is expelled. Try to search for it in the forum; although I don't think a solution for it was found. It's something in R:TW's core-engine: the EB team cannot fix it.
Bookmarks