Genghis is another person on the forums who seems to know a bit about it
Only a little, by virtue of doing a few beach landings and failing to land myself in trouble.
The legal position w.r.t. landing between the high and low tide marks is ambiguous; that land is legally crown property, but I've never heard of anybody asking for permission, nor of anybody getting in trouble for failing to. Sand and salt do get in everywhere, and if you are in a wheeled aircraft do make absolutely sure that you hose out thoroughly the wheel and brake assemblies with clean water afterwards.
I'd personally avoid landing above the high tide mark - dry sand gets in everywhere and has considerable potential to do damage - probably more so in a helicopter than a fixed wing due to the inevitable effects of rotor downwash.
Like
Vfrpilotpb I've landed at Pilling sands a couple of times, nice site - absolutely huge, but worth talking to one of the local airfields that use it for training so that you know the local practices and don't upset anybody. I've also landed at Barra (outer Hebrides) which is tremendous fun, but not as dry as Pilling. Other beaches, I've always walked first on the same day, so that I can identify an area of dry sand (ideally surrounded by really smelly rotting seaweed, since that tends to reduce the risk of finding any humans there when you arrive).
G
N.B. I made the mistake of mentioning to a FW instructor some years ago whilst overhead Pilling Sands that it must be a great place for PFLs. He agreed, and without further discussion switched the engine off! I'm glad to say that my landing was excellent, and the engine restarted first time
N.B.B. I filed an Airprox once after flying non-radio off a beach on the West Coast of Scotland. I put my altitude on the form as 900ft QNH. The Airprox investigator phoned me up later and asked what setting I had...
"I don't know, I didn't note it"
"Then how do you know it was QNH?"
"Because it read zero sat halfway between the high and low tide points on the beach I took off from".
(pause)
"Not sure about that, I'll get back to you" (he didn't!).