From what I remember from the NDKC forum the beach is private as such, not public (a rather large number of beaches in the UK are private, owned by the MOD, and even noted upon in the Coast program). The beach was given to Christies after WW2, if they don't own it they certainly control it on behalf of Crown Estates. All other beaches are owned by the Crown Estates and they often pass control to the local council, who can then ban kitesurfing. So unless you can hover down to, and set your kit up below, the water mark, you do as the controllers of said beach ask. Spooky, surely you haven't forgotten yuor debates with Glyn ......