Thanks Mark, I've been unsuccessfully using my rear shock C spanner. Seems to fit ok. I thought I'd give it another go this morning and moved the stanchion up to get better purchase. Turns out it is the steel indicator assembly that is bonded to the nut, not the nut to the stanchion as I had thought. I can get the nut off now at least, service the forks and can deal with the indicator after.
Thanks for your help guys. Saved me from using the Series III hammer and it's inevitable consequences.