Most of the foreshore - between low and high tides - is owned by the Crown.
The Christie Estates, which I presume owns the beach above the high tide mark, has a sign up prohibiting land yachts, dune buggies etc and threatening a £2,000 fine and future bans on vehicular access to the beach for miscreants.
When I was a lad the old man managed a farm on the south coast which included a beach. I seem to remember that access was strictly private and included the beach/foreshore down to the
water line, be it high or low tide. This sticks in my mind specifically because it was apparently different from the normal law regarding access to coastal land in just a few places around the UK, obviously including that estate.
Regards, SD..