almost a every day event heading down over France, aircraft out of contact for a few minutes. you hear the French controller try to call aircraft xxx, 5 mins later you hear them call on guard, followed by them giving you a turn onto heading xxx due military activity! by this time aircraft xxx contacted on guard and told he will be intercepted. Airline then gets big bill and French air force training budget covered!. Not that common in the UK but i believe the airline still gets the bill.