Go native for the finest oysters

Here's an easy test to define a great oyster from a standard one. Eat a native oyster and delay your sip of stout.

It will leave a tingle of marine flavours in your mouth for up to 15 minutes and is one of the greatest fish-eating experiences. A Pacific "rock" or gigas oyster will never resonate such intensity.

Visually, telling the difference between the two is easy: Rock are an elongated tear shape; natives a round disc. You pay more for natives because they grow slowly.

Like chicken, flavour is enhanced by maturity. Rock are farmed, with the spat (or babies) reared in hatcheries. Natives are ranched, meaning that the spat are caught wild then placed in conditions ideal for growth.

Size is important. It is not always best to order the biggest on the bar. The massive size one, which may be seven years old, is too much of mouthful for most; size two or three is ideal.

How your oyster is stored and opened at the bar is also critical - hence my choice of the three oyster bars, below. Keep in mind that the wrong oyster, badly handled, is a very expensive, and potentially dangerous, mistake.

WHERE TO EAT OYSTERS...

Murray's
This stall is to be found by the Duke of Cambridge pub, 228 Battersea Bridge Road, SW11, Thursday, Fridays and Saturdays only. (07790 605 914 www.murraysfreshfish.com)
A dozen size-three native oysters, £18. Bring your own bread and butter.
Former fisherman Richard Murray buys from the Colchester oyster fishery in West Mersea, Essex. This is not a grand event; Murray's is a simple stall selling extra fresh, sustainably sourced fish mostly from the South Coast. The native oysters are outstanding, however; well-iced, clear-looking and excellent value. Buy a Guinness from the pub next door, help yourself to lemon, Tabasco or shallot vinegar, and talk fish and other matters with Richard. Perfect.

Bentley's
11-15 Swallow Street, W1 (020 7734 4756, www.bentleys.org)
A dozen size-two native oysters, £31.50; includes bread and butter. (Irish natives also available)
Since Richard Corrigan took over, Bentley's leads again as the place to eat oysters in the West End. Sourced from Maldon, West Mersea, care is taken to serve oysters extra-icy cold to prevent any unpleasant milkiness; flesh is extremely muscular and powerfully flavoured. London's finest oyster barman, Filipo Salamone, opens the oysters, sniffing for freshness, checking the inner shell for clarity and shine, and flipping them over to test muscle tone. Corrigan's wonderful Irish bread and yellow butter is worth a trip alone.

Sweeting's
39 Queen Victoria Street, EC4 (020 7248 3062)
A dozen size-three native oysters, £25.50; bread and butter costs an extra 40p
Former Leadenhall market fishmonger Dick Barfoot deserves praise for only serving natives; an atmospheric bar that is packed with city workers at lunchtime. Oysters are sourced from Michael Dawson in West Mersea who Barfoot claims has the East Coast's most favourable growing conditions.