Telephone: 020 7437 7221
Address: 23 Lisle Street, London WC2
Open every day from 12pm to 3am. Dinner for two, with beer, £65 (though it would have easily fed three four).

I remember a time when my day didn't start until 11pm, when five or six nights a week I'd be up west, living it large and legless. I remember the time, and it was called My Youth. It was great and then, quite suddenly, it was enough. Through those Naugahyde-banquette and sweaty-walled club years, Soho at night was still the preserve of freaks and fashion victims frequenting fetid after-hours dives. Now, dancing to a corporate beat, it is mostly good clean megabuck-spinning fun.

Me and late-night London W1 have long since lost interest in each other, but tonight, on a rainy January Tuesday, I'm still out at 11.30pm with a mission and a notebook. The streets are busy, slippery rinks for besuited beer boys eyeing up the leggy panda-eyed escapees from the local chorus lines. It is, quite patently, still the chunk of the city that doesn't want to sleep, or know how to - a location to inspire at least a clutch of moody adjectives and cheap Chandlerisms, if only one weren't quite so challenged by the prospect of MSG at midnight.

Then I'm stopped by three very young people: "Scuse me, do you know where the Blah Bar is?' Of course it might not have been called the Blah Bar; it might have been the Blip Bar or the Bra Bar or the Blair Bar, but it matters not. I shrug and smile the smile of a woman fighting both a high-tog addiction and crow's feet, while the kidz laugh the laughs of young people who still have several hours left on their stimulant meters. But then my dining companion, Madam, blows it by muttering, 'Well, I know where the Blag Bar is!' Shush! We're in danger of looking like Edina and Patsy auditioning for Popstars .

In the dim past, a late duck and rice and beer in or around Gerrard Street was just one of the many pit stops during a typical night of free-range hedonism - cheap fuel, if not much of a feast for the senses. But tonight I have a hot tip: the New Diamond on Lisle Street has a reputation as an after-work stop-off for steamed-out, seared-off chefs, so is presumably a cut above mein usual choice of chow.

They are very nice at the New Diamond, an unprepossessing sliver of a restaurant last decorated in, perhaps, the late 80s. Particularly charming is the manager, Mr Lam, who allows our photographer a great deal of licence in exchange for a promise that he will receive a copy of the article to display in the window, next to those from Time Out and The Independent . Once he knows our game, he is also keen to make creative suggestions and lead us gently off-menu.

Useful, this, because my decision-making faculties are failing me, though fortunately Madam knows where she wants to go: wind-dried sausage, provenance obscure. It takes her back, she says, to the days of being wooed by a gentleman of Asian extraction who told her that the best stuff in Chinese restaurants is always off-menu. Which perhaps goes some way to explaining the presence of the Boiled Geoduck with Jelly Fish. Mr Lam comes to the rescue: 'Geoduck from the sea, like elephant's nose!' He smiles, waggles his arm in elephantine mime, 'With jellyfish.' It costs £18. In retrospect, perhaps I should have ordered it, but I like Mr Lam's Dr Seuss-ish vision of Geoduck and don't want to be disappointed. Instead, we settle on steamed scallops, plus 'salted spicy squids', 'half a roast duck with yam', 'sliced beef in spicy hot sauce in bird's nest' and 'fried mangetout leaves' in oyster sauce, with boiled rice. Which, unsurprisingly, turns out to be enough food to feed a chorus line.

At 12.30am, there is no inclination to indulge in the kind of critical waffle that involves using words such as 'piquancy' or 'zest', when a perfectly straightforward 'Mmm' or 'Euuurgh' will suffice. Thus, at the risk of doing the New Diamond out of the adjectivally piquant review it undoubtedly deserves, I shall tell you that the scallops turn out to be huge, though of almost exactly the same consistency as a school gym mat; the roast duck with yam is rather more of a yam with roast duck, only inspiring a faint 'Mmm' when soused in soy; the sliced beef is tender and delicious; the salted spicy squids are salty, spicy and squidgy; the fried mangetout leaves are, as Madam puts it 'definitely very good for you', and the wind-dried sausage is like zingy biltong, though none the worse for that.

We drink beer and eat 50 per cent of the meal, while Mr Lam keeps a solicitous eye on proceedings and the room steadily fills with the kind of ladies of the night (and their companions) who aren't, really, but very much want you to think that they are. I can't spot any off-duty chefs, but then I guess they don't consume elephant's noses while wearing their names embroidered on their chests. 'I'd definitely come back here,' says Madam, whose Mmms far outnumber her Euuurghs. I agree I'll happily return to the New Diamond_ any time between the hours of midday and 10pm any day of the week. But at midnight on a Tuesday? To be blunt, one's constitution is not what it was.

In bed by 2am, I am kept awake until three because, apparently, Steps is rehearsing a new routine in my Soho stomach. And then, when sleep finally kisses me, the upshot is a series of darkly disturbing cheese dreams... and not a single dairy product to blame them on. That didn't used to happen in the old days but, back then, I'd never heard of Geoduck either.

· Jay Rayner is away