I made a lucky guess and decided to pull out the halfshaft that
a) had the biggest oil leak b) i could get at without moving the landy
and it turned out that was the broken one (the short rear one). It had snapped right at the hub end too so it was easy to pull out :)
However it has chewed up and seemingly welded up the bearing nut, so that isnt coming off in a rush - and it looks like it will need a stub axle too.
I've cleaned out all the lumpy bits, and hopefully not too many of them have gone into the roller bearing.
Am going to go out on the scrounge tonight and see if i can find a halfshaft - thought it looks like a new one is only £15 which aint too bad.