Thanks, that has to be it. I can't see any justification for N = NO in the BRB. Yet another dubious ST clue in my opinion. There were a couple of others that I wasn't thrilled with.
I had a few quibbles too, Ken. I think n for no is fine though, even if it's not in the gospel. Filling out forms online for example, you see y or n often.
Stuck on two four-letter words! - any help appreciated.
5a Horse around in sarong on holiday (4) - C - G
26a One sought by the cops about electronic tag (4) N - M -