My ex-colleagues tell me that things have moved on - ADS-B is good for 3NM separation. They also tell me that it feeds the radar plot along with the other sensors so controllers don't know the system is using it. If the SSR coverage runs out the they will see an ADS-B symbol (Apparently the system will display an SSR symbol before an ADS-B symbol when both are being received). I also got the impression that the ATCs cannot select what they are looking at so would have been unable to do the check of ADS-B as Dick wanted.