The distinction between intelligence agencies or international groups may be slightly moot on occasion. Secret Societies are a very influential element of the deep state. Making up much of the political establishment, media and intelligence.
An Oxford university dining club with a habit for inebriation and subsequent property destruction. A UK equivalent of the US Skull and Bones fraternity, which has had a large number of establishment insiders as members over the years.
The Knights of Malta are a Roman Catholic military-religious order and/or secret society of, traditionally, a military, "chivalrous" and "noble nature". It is the one of the world's oldest orders of knighthood, dating back to the 11th century. The Sovereign Military Order of Malta is headquartered in Rome, and is arguably a sovereign subject of international law.
The most elite US secret society, largely unknown until its influence was publicised by Antony Sutton, who highlighted in particular its members' apparently insatiable desire for power and their mutual loyalty in spite often of public antagonism.
A very low profile group that has been in operation for over a century and has Elizabeth Regina as its patron. Members include ministers, diplomats, CEOs and others. Who knows what this "dining society" discusses over dinner?...