This whole incident has convinced me to buy a Zaon PCAS device and interface it to my G496. Seems like $1700 is a good insurance policy, and HAD I been the "other" aeroplane in this sad incident, it would probably have worked quite well (i.e. all commercial twins will have Mode S).
If you look at:
WebTrak: Bournemouth and choose 11:45 on 28th July and look to the top left (near Blandford, may have to zoom out or move map) there are two aeroplanes, one transponding 7370 which come pretty close. 7370 was me, and despite what the altitude readouts say we were pretty much at the same level. We didn't see each other until it was pretty close, and he saw me before I saw him....it was a "whites of the eyes" moment.....