Well then, first several attempts got me to 12off, coming back the next day down to 4off and that took ages.
Edit: Two months later I tried a different move and came down to a 2off. After frustrating ages I realised I was going round a block when all it needed was pushing out of the way. Sorted.
I notice that there are two solutions, but they are relatively similar and they both retain the interesting bits of the solution design, so I guess I'm fine with it.
