Well, the hub works perfectly now I've realised the problems - the right cone was a quarter of a turn too tight and the indicator spindle is wrong for this axle length (different to std Brompton, which I think are made specially) so I just set it up using the "little chain just tight in top" method.
It does, however, leak like a good'un from the ball ring, which is a different design to the old AW. I'll probably have to strip it and pack it with the special grease, but I'll keep going for a bit in case it's just overfilled.