Safety advantage..... not from the CAA !
As some one who has Mode S in one of my aircraft I can tell you that it provides no safety advantage what so ever at the moment there are only two radar heads that can use Mode S, in short if a low powered Mode S transponder is not within 30 miles or so of these radar heads it can't be "seen".
The safety advantage of mode would be WX and traffic data link this system would give light aircraft a a WX radar picture and a TCAS like system but have NATS/CAA mandated the instalation of the ground based equipment for these systems ? like hell have they.
Untill the authoritys start to install the data linking of these safety systems the argument that Mode S is a safety mandate is bankrupt.
So far the mode S thing seems to be driven by a need for some parts of the CAA to to keep them selfs in a job, once they have the Mode S thing in the bag they will form another commitee to spend two years "consulting" to force another bit of usless kit on light aviation to protect CAA jobs.
Tangovictor you are sadly mis informed the CAA won't be installing the kit to keep you clear of the military fast movers!