rod 1
The practical requirement for the run and break is a military one the object being to keep as much energy in the aircraft and there for the ability to manoeuver if attacked untill the last moment and to only slow up when over a well defended area when the local triple A should be able to ward off an attacker.
This is hardly a factor over most UK civil airfields.
I dont object to pilots performing a run and break BUT all the pilots in the circuit must know what to expect , if any any doubt exists then a normal circuit join should be performed.
If the run and break is part of a practice of a display then ATC should keep the circuit clear untill the practice has finnished.
The bottom line is that aircraft performing high energy manoeuvers and pilots in slow aircraft without a proper briefing cannot safely mix in the circuit.