“I hope to God we’re not going to be the next Burnham Market,” says Ian the Stockbroker. “We used to have a cottage in north Norfolk, but we got fed up — you’d go in the village boozer and meet nine chinless wonders from the City in the first five minutes.”

We’re at the Oyster Bar on Mersea Island, off the Essex coast, sharing a table strewn with mussel shells and lobster legs. Opened three years ago, this plank-board shack beside West Mersea boatyard has a considerable reputation — and it’s only the second trendiest restaurant in town.

There’s also the Company Shed, an even scruffier seafood paradise just along the harbour. Sel Yucer, the Oyster Bar’s shucker-in-chief, confirms that, last summer, the queue stretched along the quayside for an hour.

On the face of it, Mersea makes an unlikely upmarket retreat: five square miles of salt marshes, creeks and low-tide slop marooned on the margins of England’s most maligned county.

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It’s a real island, too, bolted to the Colchester coast by the Strood, a Roman causeway that often floods at high tide. But this is not the Essex of disco balls and white stilettos — more a place of orange sun suspended in glassy water and red-stilted oystercatchers tiptoeing through the shallows.

The reason for its gallop towards fashionableness is tinkling away in the Oyster Bar’s back room. Tall ranks of tanks overflow with Mersea native oysters, raked from the muddy creeks within sight of the restaurant window and sluiced by a perpetual waterfall to clean them up for guzzling.

The Oyster Bar is one of the cheeriest dining experiences I can remember. It’s a fresh-scrubbed, smiley-staffed, canteen-style place where you hang your jacket on your chair and order at the kitchen counter. Which is handy if, like me, you decide you want half a dozen oysters to start . . . and the crab chowder . . . oh, and the baked scallops, please.

When I go back for the third time, Chris the chef not only grins indulgently, he brings my scallops to the table in person. It’s an Ikea job, loaded with a squeezy bottle of ketchup, Tabasco and kitchen roll for when the pleasure gets too much and starts oozing down your arms.

It’s a forlorn February afternoon out of the window, and it suits West Mersea. A town of sail lofts and sea walls and gently exfoliating houseboats, it’s full of the frayed-round-the-edges fascination you often find in boaty places. Some of them have perky pastel paint schemes, but most look like wrecks, listing over in the low-tide scurf of estuarine mud.

The gangplanks across the marsh are hung with laundry; here and there, crooked stovepipe chimneys belch wood smoke. It’s a strange gypsy universe that you feel must have its own rules, its own religion, maybe.

And I start to think that perhaps Ian the Stockbroker needn’t worry. According to the Mersea Island Guide, there are still only seven bed-and-breakfast rooms on the island. True, it has a vineyard, a microbrewery, an “art cafe” and two world-class seafood joints — but no matter how much Mersea tarts itself up as a destination for foodies, you can’t really gentrify ooze.

AT THE ISLAND’S vineyard and microbrewery, where I call next morning, a rack of postcards shows cars aquaplaning across the Strood. Lately, a debate has been raging among Mersea natives about the height of the causeway. Raising it by just a yard or two would prevent its daily immersion, but the locals enjoy being cut off. They like the sense of strangeness island status brings.

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