If that was actually a near mid-air, ATC was entirely at fault.
Oh!, The certainty of those with apparently limited experience.
Actually, it wasn't an ATC fault at all, the offender was the aircraft taking off, and on that day, (as every other day, really) ATC was depending on crews to adhere to their clearance, which, in this case, was "cleared for immediate takeoff", and we heard the clearance at about 4nm. The aircraft on the ground didn't comply with the clearance, as we became visual at about 2/300 ft., it was just starting to move.
ATC had no ground radar at the time, and, in theory, has provided necessary procedural separation. With us going around, and the other aircraft climbing up underneath us, "director" broke into the tower frequency, and gave is the immediate left turn already mentioned.
Given the very wide variety of actual standards of crews operating in UK airspace, to this day, UK NATS and local controllers do a remarkably good job.
Tootle pip!!