SASless, we have TCAS, as do an increasing number of UK operators.
TCAS is a great help but it is only a part of the situational awareness equation. A radar info service is another part, as is listening to and speaking on the radio on the appropriate frequency. But you know all that already, MG.
Best not to cast aspertions before knowing the facts, so I won't comment on a particular case. However, I don't agree with people carrying out ad-hoc GPS letdowns per se, if for no other reason that the CAA doesn't allow it. Is it possible that some of these aircraft are being flown on VOR / DME / ADF letdowns that you are unfamiliar with?