I can't see how a FIS can be of any value whatsoever in spotting traffic.
Another aviation myth, propagated through the decades and taught to all PPLs...
"Hmmm. I am flying over Kent. London Info tell me there are 11 planes known in the area. Gosh, if I keep a real good lookout I will be able to avoid them". How big is this place? Must be several thousand square miles, and several thousand cubic miles of air between surface and the base of CAS.
Time to duck again!