Birds seen at RSPB Medmerry

Good morning, my first post here so hope I don't make a mess of it! Saw a pair of these on the beach between the coastal defences at the Breach end of RSPB Medmerry. The one pictured here was foraging in the seaweed, its mate was confining itself to the stone breakwater. Our first impression with the naked eye was rock or water pipit but with binoculars it didn't seem to fit the bill, lacking any black streaks on the breast. We only saw its mate in silhouette so couldn't see any markings.