re: I thought the Brits were pretty forthcoming about crop circles (and ufos')
Probably the ridicule factor.
In some circles, it's still considered an untouchable subject.
As for Buckingham Palace, perhaps they thought that Colin Andrews was using the royal family to peddle his book or movie.
Larry King has done many fascinating shows on ufos and there is plenty of specials on the History and Discovery Channels. If people would just watch it and keep an open mind, then they might learn something. A lot of it falls into categories that our own science has yet to explore or explain.