I've seen and been involved with similar situations at Heathrow between traffic landing on 23 and 27L.... No problem. Controllers don't "scramble" to sort out problems. Providing the aircraft can be clearly seen by the controller(s) concerned there is no laid down separation standard and clear instructions are issued to resolve any conflict. Surely experienced pilots know this?
I don't understand the bit about the controllers seeing the flights merge on radar. It was daylight and "VFR" so were these tower controllers or radar controllers downstairs in the dark? Tower controllers simply look out of the window to see that aircraft are safe - the fact that they may merge on radar is irrelevant.
Sounds so much like the "4 seconds from disaster" situation I was involved with at Heathrow. Nobody knew about it until the trash papers' 6 inch headlines next day.