Tiny brown bird with white spots

Hello, just wondering if you could ID this little brown bird for me please? It did not appear at all mottled but had tiny white spots on its side, very inquisitive and regularly coming closer to us, movements reminded me of a robin. Pecking at the seaweed, lots of sand fleas around so possibly eating them, partner thought possibly a winter wren. Seen on a beach in Flotta, Orkney.  Apologies for the picture quality, it's a zoomed in video still!