Conrad Gallagher is a shrine to stylish dining, but its high prices and indifferent service are enough to quash your appetite

Around the time we were in Conrad Gallagher in London, running up a £125 bill for dinner, Conrad Gallagher was settling his debts in Dublin. The name may not mean anything in London, but in Ireland the celebrity chef's a big noise. His Peacock Alley has a Michelin-star, his latest cookbook One Pot Wonder is on sale in bookshops and ready-signed in his restaurants, and his tax liabilities have been widely reported. We ate well enough, but paid up and left wondering whether London needs another absentee chef's large, expensive restaurant with seats to fill and some fine tuning still to be done to the wine list, service and cooking.

Gallagher's West End gig has the backing of Vince Power of the Mean Fiddler music organisation, whose events, such as The Fleadh, are more closely associated with liquid refreshment than refined solids. What you see through the glass front at the tree-shaded end of Shaftesbury Avenue is people drinking cocktails in brown leather swivel chairs – the restaurant's underneath. When my consort arrived he asked, "Do we have to stay?" "But I've finally got a drink," I pleaded, "and we're booked for dinner in 10 minutes; they couldn't fit us in earlier."

Downstairs, past a kitchen visible behind a glass screen and through an invisible curtain of cooking smells, we were in a cavernous, underpopulated room of tables covered with a vitreous crop of large glasses and a single, absurdly long-stemmed flower reaching towards the low ceiling. Why then, when I rang to book a table at 8.30pm, had I been told that 8.45pm would be better?

Nightlights flickered on a nearby bar like miniature strobe lights, the men at the nearest occupied table loosened their ties and got noisier, but the restaurant never got fuller. If our jaws had hit the ground when when we saw that starters cost £9-£14, and main courses £17-£24, it wouldn't have been a soft landing. The floor is gloss-painted concrete. Hunched on a low banquette over a table wide enough for four, this hard-edged environment seemed not so much funky as skew-whiff for the type of cooking.

Its aspirations are revealed by an exhaustive litany of ingredients. "Can't we take it as read that our food will have salt in it ?" wondered my consort, pointing to the inclusion of sea salt with the roast fillet of beef with foie gras, Napoleon of vegetables and truffle. Several dishes included at least one flavour more than seems wise – terrine of duck and foie gras with crispy spinach, mango and chilli, apricot with truffle aïoli and toasted brioche, for example. And the menu terminology also shows that chefs don't necessarily not talk the same language as us. They say emulsion, we think of the paint shop next door. They say squash foam, we say, "Yuck, I'd rather not sink into that." I'd have ordered the fresh pea emulsion with fava beans, baby lobster, coconut and tomato had it not been for the coconut. It's challenging enough to find the focus of each dish when you're reading the menu, let alone when it comes to eating it. Though when it did come, the halibut fillet – on soft and sweet creamed leeks, with baby veg, for crunch and contrast, and a ribbon of red wine and scallop dressing, to tie up the subtle package with a nicely sharp tug – was one of the dishes that left our misgivings unrealised.

After an espresso cup of frothy squash soup with summer truffle, our starters arrived garnished with the kind of bubbles that make you suspect someone in the kitchen has a grudge against you. Froth on top of anything other than a cappuccino looks like spit. On both plates, under the frothy topping, there was more squash. A butternut squash risotto with trompette de mort mushrooms and spinach leaves was keenly and wonderfully seasonal and would have been as rewarding without the hard-to-identify rolls of rabbit wrapped in spinach dotted around it. Remove the rabbit and you'd have satisfied any vegetarian, too, though there's a separate organic vegetarian menu for those who ask. The contents of a crab raviolo, a substitute for the advertised langoustine, were slightly dry, but the squash purée underneath and spinach purée on top also showed that the cooking has polish, as well as spit.

Next, rather puzzlingly, we were given a passion fruit sorbet. At every stage numerous staff seemed to appear, and then, as they so often do, vanish by the time we wanted the bill. The maître d' could try softening his approach. We'd been told by someone else which dishes were off, and then promptly forgotten. "May I have the turbot?" "No."

Restaurants with this calibre of cooking – and, of its type, it certainly shows skill and commitment to the cause – ought to have staff that communicate the kitchen's passion. Ours did so only half-heartedly. Someone in a grey Nehru jacket went through the motions of telling us what was on a square glass soap-dish of a dinner plate. "That's fig, that's duck, that's foie gras, what's that?" said consort, carrying out his own inventory. "That" was a wonderfully delicious buckwheat and walnut cream, a herby, nutty, stock-simmered, risotto-textured accompaniment to pink duck cooked with honey and soy, duck liver parfait (not foie gras), poached fig and baby carrots, asparagus and turnips.

For £7.50 a crême brulée, it should be better than mayonnaisey, even if it does have petals of spiced pineapple arranged around the wide rim of the dish. Hot chocolate fondant with pistachio ice cream was a preferable version of another modern classic pudding, though it came with what's obviously Gallagher's signature – a dollop of frothed up pistachio. Petits fours with coffee further sweeten the impact of the £60-a-head bill.

It's not just a lot of froth; underneath it all Conrad Gallagher's food is serious and often successful, but the aim of bringing it to London's attention might be better served by a more intimate acoustic arrangement rather than this nightclub-scale showcase.

Conrad Gallagher, 179 Shaftesbury Avenue, London W1 (020-7836 3111) Mon-Sat lunch 12.30-3.30pm, dinner 5.30-11.30pm. Lunch, and pre- (5.30-7pm) and post- (10.30-11.30pm) theatre menu, £18.75 two courses, £23.75 three courses. Major cards accepted. Wheelchair access