Having worked the English Channel sectors as a Military controller, embedded within the LATCC Ops Room, i can imagine the disruption that caused at FL 295 or whatever.
I think the most polite phrase I could use is "Not a very good idea from a safety aspect", especially if there's no Mode C to give anyone a clue (although I assume the escorting aircraft would be so doing). But it used to require substantial effort to thread Mil traffic through that airspace at any level, coordinating with everyone and anyone. An uncontrollable 'unknown' requires EVERYONE to get out of his way, and that in NOT a bit of airspace where you want to do that.
I recall the Lakenheath Wing, doing French Low Level activity, bugging out due to weather and climbing out of France to go home through the Seaford Sector ... no flight plans, no pre-warning, just a dozen or more aircraft popping up on frequency needing to climb and go home through all the airways. Happy days of the great Civ/Mil relationship at LATCC
