A Forgotten Shipwreck on Gullane Bents (East Lothian)?

If you turn to Google looking for a shipwreck on Gullane Bents, in Scotland, chances are that most search results will direct you to two historic midget submarines wrecks, which lie half-buried in the sand of nearby Aberlady Bay, and can be visited at low tide. Wading along the picturesque East Lothian beach yesterday, however, I came upon what from a distance looked like a rock. But on closer inspection it was clearly man-made, forged of steel, and similar in appearance to the entrance hatch of the abandoned midget submarines along the coast. There’s no evidence (that I know of) of such a vessel on Gullane Bents, and it’s likely the explanation is rather more prosaic. But if you do know more about the history of this apparent maritime relic, we’d be intrigued to learn more. Is it a forgotten shipwreck from a bygone era, or something else?