Well, I bought a 1/2" driver in Lidl since that was the only size they had left and a socket set in
Halfords. It's a bi-hex (12 point) but all they had. I wanted to buy an individual socket but it was the wrong size - 3/8. No doubt the extra sockets will come in handy some time. I did take notice that the socket needed to be slim to fit in the crank head.
When I got out the crank extractor I noticed it had a hex wrench on the end - doh.
The next problem is that one of the chainguard bolt heads is rusted; I've got some ideas up my sleeve and I'll sort that tomorrow.