Contributers are now aware of UK circuit procedure.
For the case in point, using the debris sites photographs and the low 5 kt wind, a (say) 90kt collision at ~1000 ft. could allow the broken propeller to travel perhaps 1/4 mile.
But the end of runway 20 is at least double that distance away, which implies impact occurred whilst the climbing a/c was already on his crosswind leg.
This suggests the Vans pilot followed correct procedure - taking off he'd turn left at ~500 ft in a climbing turn to continue to circuit height where he could leave (or rejoin the circuit). The joining a/c lost its prop. when striking the Vans from behind in its pilot's blind spot.
Ergo neither pilot was aware of the others likely proximity despite ATC radio ?