Number one best cellar

What better, angels, than to dovetail a review of the new Harvey Nichols restaurant with a little light shopping? Having shopped till the staff were popping up behind rails hissing "We're closed now, madam" (meaning "Leave, bitch, or I'll scream 'she is cellulite ridden'"), I made my way to the basement, hoping to glide effortlessly from retail to oral therapy. Alas, a nightmare of confused directioning, worthy of the sign posting system in central Reading, led to the wrong entrance - the one to the Fifth Floor bar, cafe and restaurant extravaganza, whose success has encouraged expansion into a new posh restaurant in the basement site of the former Joe's Cafe.

Exhausted and drained by my quest for the door, though still, essentially, brave - I eventually located it on the east side of the Harvey Nichols building. Foundation seems an odd name for a store restaurant, with its unattractive suggestions of sturdy undergarments, or thick, matte facial colour but of course, on descending the staircase, the meaning becomes clear - the whole design rationale is to make you feel you are in the foundations. It is a dimly lit, low ceilinged underground space dotted with air-con vents and smoke alarms and water pouring down one wall behind the bar in a really quite convincing imitation of someone upstairs having run the bath over.

Any fan of Absolutely Fabulous would expect to find at least a smattering of Luckybitches with white suits, orange faces and big hair, rasping at the waiters, "Glass of Bolly, darling, don't give me Moet because I'll know." But the clientele was more the sort at which Patsy would hiss "Shopgirl!" There were lots of tables of girls chewing on plastic cocktail stirrers, blowing smoke out with mouths in complicated shapes, here a fake Prada bag, there a pair of on-head sunglasses. Everyone, but everyone, was in black. There were more goatee beards than on the entire cast of The King and I, though not - as yet - on the girls (watch out for the female goatee in the autumn!).

My friend, who knows all about design, was not impressed. "Very late 80s. No texture, flat colour, ambient light full of graphic cliche. Ugh. I just knew there'd be one green or yellow wall." I foolishly ventured that the room was pleasingly New Yorky. "You think this is New Yorky!" he cried incredulously. I must admit it didn't seem to be exactly at the cutting edge of restaurant looks and personally, I'm never keen on a basement, especially a low ceilinged one, where the prominence of sprinklers, vents and smoke alarms has you checking the fire exits before you've even sat down. The point was, though, Foundation had only been open a week, and you could tell it was going to be a success. The whole Harvey Nichols operation is extremely clever at spotting and offering exactly what young people with money want. Good, trendy food, nice, if pricey drinks, and a place for young trendies to meet others in stylishly understated surroundings, with the weight of all those storeys of clothes pressing down, is clearly going to prove irresistible. Furthermore the lighting in the ladies' loos makes you look pretty, which, what with the waterfall over the bar and all the booze on offer, is very important.

Head chef Graham Grafton, formerly sous- chef at Chez Bruce and at the Fifth Floor, under the award-winning Henry Harris, is one of a group of chefs who have spread out from the Bibendum stable. Staff have the same winning blend of professionalism and friendliness which works so successfully on the Fifth Floor.

It seems rather hard, therefore, to force the poor waiters to stagger under the weight of menus encased in thick sheets of perspex held together by screws (thereby eliciting another "late 80s" snort from my companion): inappropriate for such a light, well thought-out list, a modern British mix with lots of seafood and Mediterranean influences: mussel and saffron risotto, meze, Bayonne ham and goat's cheese, sea bream, saffron butter beans, fennel and aioli, rabbit with wild mushrooms. There is also a separate yakitori menu.

I started with excellent and beautifully presented mixed yakitori. There's something wonderful about enjoying Japanese food just for a starter, knowing you're not then going to have to fry meat at the table, or eat yaks' curd when it comes to the main course. With the problems of the national herd much in our thoughts we were in a decidedly fishy mood. My date raved about not only the taste and texture of his pan-fried mackerel which came with sushi rice and spicy cucumber but also the on-plate design: a great tribute to the chef.

For my main course I enjoyed a superbly grilled piece of tuna, cunningly whipped out just at the point when it's still melting in the middle. It was served with what can only be described as crisps - which I always find disappointing almost the point of the hurtful. But it was easy not to mind too much if you thought about all those size 10s upstairs, and my date's baked cod in a basil crust was "just lovely, really, good." Foundation is clearly going to offer assured, stylish, tasty cooking at the more affordable end of the posh restaurant bracket (starters under a fiver, pounds 11.50 for a steak).

Unfortunately there was something about the boozy bar atmosphere, and the hovering ghost of Patsy, that made us rather let ourselves down. Having started with cocktails, then moved on to a splendid bottle of Pouilly Fume, before we knew where we were ordering another one. My notes on our desserts, which I firmly believe were vanilla creme brulee and cheesecake with grillotine cherries, were as follows: "vg, v. creamy mm, blurry goo." Lurching happily across Knightsbridge, dodging the cars, we agreed that despite our initial snooty sneers, we had blurry gootime and woshdefinly go bagagain. Yur. !

Lower Ground Floor, Harvey Nichols, Knightsbridge, London SW1 7RJ. Tel: 0171 201 8000 Open Monday to Saturday, 11am to 11pm, and Sundays noon to 6pm. Average price per person, pounds 25. Set lunch, pounds 10. Credit cards accepted