Sitting at the top of the French hill I have seen and spoken to a/c that are/have been intercepted by the Military. In ALL cases I check that the pilot is/was aware and every time have had an AFFIRM reply.
If the interception was for training purposes then every a/c was ASKED first, and French civil control identify and handover any still intercepted approaching the boundary.
If it wasn't a training situation, then someone isn't speaking to Civil control, so initial RTF failure procedures have been enforced - you can file on being intercepted, they will already have filed back for loss of communications. All will be investigated together and the reason for the lack of communications sought.
None of the interceptions will interfere with TCAS RA's as Mode C on the fighter is disabled. You could get a TA, but the way in which interceptions normally occur, TCAS will assess 'no risk'.
Arran's view - when and where did this incident occur?