Yes the RAF have fited TCAS and this is a big improvement in safety but the whole point of this thread is about the mandating of Mode S and the supposed safety improvments that the CAA is using as a reason for pushing this along.
So far the CAA has failed spectacularly to prove it's safety case for Mode S above Mode C, the safety issue is just a smoke screen to cover the issue that this implimentation is just jobs for the boys at the CAA.
If the safety was the real issue at the CAA then we would have the WX & traffic data link installed, this would bring TCAS like indications within the reach of most light aircraft.
The mode S issue would be a lot less of a hot potato if the issue was one of safety and it was being introduced with some improvement to GA safety but it is not of any improvment what so ever over Mode C.