It's a filter-feeding mollusc that feels like a briny bolus of mucus slipping down your throat. Encounter it at the wrong time of year (during the spawning season - any month without an 'r' in its name), and you'll be swallowing an unappetising milky 'spat' that tastes as wrong as it feels. And all this is supposed to be an aphrodisiac. If you're the kind of Brit stirred more by a tender side of beef, you wouldn't be the first. In Victorian times, oysters were common fare among the working classes; those who toiled 'below stairs' would measure the quality of their job on how many times they ate meat, rather than oysters, each week. As Sam Weller observed in Pickwick Papers: 'It's a wery remarkable circumstance, sir, that poverty and oysters always seem to go together.' In 1912, nearly 30 million oysters were landed off British shores. Since then, disease, pollution and harsh winters have come close to scuppering the trade. But as with ivory, gold, and fair-trade food, the oyster's very scarcity has made it desirable; the Victorian equivalent of baked beans is now a delicacy. If you wish to sample the delights of ostrea edulis, native to oyster-opolises such as Whitstable and Colchester, you must be prepared to shell out - a dozen oysters at London's swanky oyster bars will set you back about £20. Yet still people melt over the mollusc. The opening weekend of this year's Whitstable Oyster Festival drew about 40,000 people to the Kentish town, which has a population of just 30,000, who subsist on burgers.