FR24 is impressive, yes? But it's only a website using secondary radar, partly from amateur spotters, using ADS-B. You may notice that a lot of mil ac are missing from the picture. You may not have noticed that the system is neither authenticated nor secure. It is an up and coming system and it has the potential to use satellite receivers.
But for the purposes you are implying, we already have systems to do collision avoidance; they just haven't paid for it to go into the entire RAF fleet.