Sorry Brendan, I didn't get it then.
Thanks Rocky, the penny finally dropped with 19ac when, like you, I got the crossers.
I've made lots of progress but ground to a halt again. Can I have a hint for 14ac, for which I have two possible answers. This might help me with 15d, for which a hint would also be helpful to get cracking on the SE corner. I'm also stuck on two in NW corner - 2d and 11ac, for which hints would help.