Ok I am assuming that there are some UK members here and that this location hasnt already been posted

This is my old vaction haunt was Harbour Cove/Hawkers Cove near Padstow in Cornwall. I Used to fly my Delats and Flexifoils here when we got some decent wind. Buggying was only just starting out so I never saw anyone trying it here but at low tide it has a huge area of flat sand (as you can see by teh light coloured area of water). The bay was also pretty popular with windsurfers so I am guessing Kite Surfing woudl work pretty well there as well. I dont know what restrictions if any there are there though.
Harbour Cove/Hawkers Cove/Tregirls

If you look at the water you can see a deep channel on the right but when the tide goes out you get a large area of flat, reasonably hard (if damp) sand that can go as far out as 1/2 to 3/4 of a mile (at a guess) or at least almost out to the Headland