Fishworks, London W1

Doesn't anybody sleep in on a Sunday morning in London any more? From the moment it opens at 9am, there is a queue outside the bakery Paul in Marylebone High Street, for coffee, croissants and baguettes. The nearby streets between Blandford and Cramer are as busy as rush-hour, as pink-cheeked couples follow the signs to the temporary residence of the local farmers' market. Butcher The Ginger Pig in Moxon Street is a joy to behold, as the staff discuss earnestly the merits of sirloin versus fillet, and aproned girls make mince tarts to bake in the old Aga. Next door, the organics store is doing a healthy trade, and next door to that, La Fromagerie is jam-packed with goodies, from Somerset cheddar to sugared Toulouse violets. Back in Marylebone High Street, there is a cookery class in full swing at Divertimenti, while across the road, Skandium is doing a brisk trade in designer cutlery.

Doesn't anybody sleep in on a Sunday morning in London any more? From the moment it opens at 9am, there is a queue outside the bakery Paul in Marylebone High Street, for coffee, croissants and baguettes. The nearby streets between Blandford and Cramer are as busy as rush-hour, as pink-cheeked couples follow the signs to the temporary residence of the local farmers' market. Butcher The Ginger Pig in Moxon Street is a joy to behold, as the staff discuss earnestly the merits of sirloin versus fillet, and aproned girls make mince tarts to bake in the old Aga. Next door, the organics store is doing a healthy trade, and next door to that, La Fromagerie is jam-packed with goodies, from Somerset cheddar to sugared Toulouse violets. Back in Marylebone High Street, there is a cookery class in full swing at Divertimenti, while across the road, Skandium is doing a brisk trade in designer cutlery.

If you need any more convincing that Marylebone is the new food central for the well-heeled, then the appearance of the very latest Fishworks should be proof positive. Since starting life in Bath in 1995, Mitchell Tonks' groundbreaking concept, combining fishmonger with fish café and cooking school, has yet to put a foot wrong in its slow move towards world domination.

The Marylebone model is the fifth so far, and keeps true to the formula with its well-stocked fish shop at the front, and Mcfriendly family fish caff at the back. On a Sunday, people don't just bring their children; their children bring their children. Buggies, high chairs and farmers' market bags are as much a part of the décor as the deep-sea blue walls and rainbow-bright art, while mid-week brings shop-workers and casual couples.

Amazingly, in a triumph of good taste over the popular vote, Fishworks refuses to offer deep-fried fish and chips. Why? Probably because a desire for fish and chips has little to do with the fish. And it is fish that Fishworks is all about.

There are three ways you can order. A printed menu lists platters of raw shellfish, whole sea bream baked in sea salt, spaghetti with clams and the signature zuppa del pescatore, or Italian fisherman's stew. Then there is a blackboard menu listing daily specials such as chargrilled South Coast monkfish, seared yellowfin tuna steak, and fillet of grey mullet. Or you can pop out front to the fish shop and choose whichever whole fish that takes your fancy.

But whatever you do, have the crusty bread and freshly made cod's-roe taramasalata (£1.95); it is the best taramasalata you will have had. Subtle, pale, creamy, moussey and lightly smoky, it is miles away from the shocking-pink travesties in the supermarket fridge.

You could also do far worse than start with oven-roasted shellfish (£8.50), served in a white gratin dish - it's piled high with cockles, clams, mussels, prawns and a langoustine, all in their shells, and all bathed in thyme-strewn, garlicky, olive-oil juices. The timing is impressive, the delicate shellfish retrieved from the heat before they lose juiciness and flavour.

Even the unfashionable mackerel, one of my favourite fish, gets the star treatment here. A plump whole fish (£10.50) comes hot off the grill, its skin crisp, and its flesh moist and flaky, annointed simply with olive oil and lemon juice. Its Omega 3 oiliness hits it off beautifully with a soft and fruity Michele Satta Diambra (£25.50), one of the few red wines on the predictably white-dominated list.

The best advice I can give to those in doubt is to have the zuppa del pescatore (£15.90). Lolling about in the copper dish in which they were cooked are a chunk of John Dory, a cutlet of hake, a section of monkfish tail and a small skate wing - all served on the bone and bursting at the seams with flavour - plus a scattering of prawns, mussels, cockles, clams and a langoustine. It's a glorious fishy feast for one or two, made memorable by rich, soupy juices pumped up with tomato and saffron, and a slab of grilled bread, without which it would technically be a soup and not a zuppa.

I only strike one real snag, when a small, whole, grilled Falmouth Bay plaice (£14.95) comes unexpectedly doused in brown nut butter, which makes its minimal flesh taste greasy instead of clean. The staff are pleasant enough, but they are a right bunch of tiddlers, and it feels as if they need the support of a few seniors to help them relax and stop bluffing.

Desserts here are not really the point - chocolate pud, crème brûlée, etc - with a fresh lemon tart (£4.95) being suitably lemony and classically made, but no more than that.

As I said, Fishworks is all about impeccably fresh fish and shellfish, simply cooked, casually served and - the real blessing - reasonably priced. You can stop by for rock oysters and champagne, gorge on whole salt-baked wild sea bass for two, with fish fingers (real ones) for the kids, or take home a feast of mussels, crabs and prawns. It doesn't have the silky service and chic crowd of J Sheekeys, or the precise cooking in classic surrounds of Wheeler's. It just does fish, and it works.

15 Fishworks 89 Marylebone High Street, London W1, tel: 020 7935 9796. Lunch and dinner Tuesday to Sunday. Around £95 for two including wine and service

Scores 1-9 stay home and cook 10-11 needs help 12 ok 13 pleasant enough 14 good 15 very good 16 capable of greatness 17 special, can't wait to go back 18 highly honourable 19 unique and memorable 20 as good as it gets

Second helpings: More eateries with fish shops attached

The Company Shed 129 Coast Road, West Mersea, Essex, tel: 01206 382 700 This simple wooden hut, tucked away in the salt marshes of West Mersea, is home to one of the best fishmongers in Essex, dealing in its own flat-bed oysters as well as local seafood. There is also an inordinately popular, no-fuss, no-frills dining-room serving up couldn't-be-fresher seafood platters adorned with nothing but fresh lemon (BYO wine and bread).

Loch Fyne Oyster Bar Clachan, Cairndow, Argyll, tel: 01499 600 236 Along with its adjoining smokehouse and shop, this marvellous place opened in what was once a cow shed on the banks of Loch Fyne back in the mid-1980s and has since inspired the 24-strong Loch Fyne restaurant operation. Loch Fyne's famous oysters top the bill, but other offerings include Loch Fyne Kippers, Loch Duart salmon, and Isle of Mull Cheese, as well as Glen Fyne venison and sirloin steak.

Bibendum Oyster Bar Michelin House, 81 Fulham Road, London SW3, tel: 020 7589 1480 Not to be confused with the higher-priced Bibendum restaurant upstairs in Michelin House, the ground-floor oyster bar is casual, easy-going and relatively wallet-friendly. It's all very simple, from the crab salad and salmon gravadlax to the fruits de mer platters. On your way out, pick up some West Mersea oysters, Guernsey scallops or live Scottish langoustine from the forecourt fishmonger, Crustacea.