Box spanner won't be good Gareth - the socket needs to be 12 sided and not 6

I've searched on all the usual tool supplier webbys and can't find anything

Maybe, If i can get a normal 12 sided socket, get jiggy with the angle grinder, weld in some box section, and then weld the top onto that, I'll have a nice deep socket

The next question is, what size is the socket I need