I've managed to bleed circuit one on all four wheels. The rears were a right pain - access is pretty tight even though there's no plate in the way. In the end I had to slacken it very slightly with a ratchet then use the spanner just to finally free it from any tension, then return it as far as I could with the spanner again before nipping it up with the ratchet.
The brakes feel a lot different now. Very firm. I'm going to take her out for a spin in the morning, although I should probably have a quick go at circuit two on the front wheels before I do that.
They were always a bit spongy but stopped it ok. I put it down to air assist feeling different to a normal brake, but now they've been bled I know that's not the case.