I have been searching through my Scott cat this evening looking for this stamp.
For the life of me I couldn't find it. I could find the 1953 version which is the 2d (scott 280) but do you think I could find one for a 40c denomination. I figured it would have to be a reissue, but .....
Anyway, I did a search and came across this website from New Zealand Post. I searched on this site for "Buckingham Palace" which led me to the stamp with all the issue info. Well done NZ Post!!