There is something about the great courtyard of Somerset House that imposes a certain stateliness of step. Hurrying doesn't seem consistent with the 18th century, frock-coated, silk-stockinged, tricorn-hatted classical magnificence of the space. Out there, in the Strand, all is hustle and bustle, fume and fuss. In here is a different world which keeps to a steadier time. At least, that's what I thought as, late for lunch, I hurtled across the paving like a greyhound from the trap. I had heard spectacular things about the food at The Admiralty, Oliver Peyton's new venture at Somerset House, and I wanted to marvel - or not- for myself.

Oliver Peyton is not a chef, but a restaurateur. Actually, he is more of a restaurant impresario, a Phineas T Barnum of restaurants. He has a penchant for the spectacular and the idiosyncratic, and I was curious to see if the restrictions imposed by Wren's grand design and the quangos who guard the spirit of the place, had restrained his visionary energy.

The answer is yes and, alternatively, no. The restaurant runs through three linked rooms in the right-hand wing at the far end of the great courtyard if you enter from the Strand. Notionally, the rooms overlook the River Terrace and the river itself, but the windows are set so high that you can only see out when standing up. But they are handsome rooms, with the characteristic high ceilings, and a curious, rather clubbish, feel to them. This may have been due in part to the dominant kind of sub-fusc green colouring, or to the stuffed sailfish and head of ibis leaping off the walls.

But you can't keep the fun out of a Peyton restaurant. Beneath the marlin there was a little case of dried sea horses and some of the chandeliers take the form of little galleons under sail. Then there was the curious decking attached to each table, adding another level on which you could put bottles of wine, dinky bread baskets or, as most people did, a left or right arm.

And there was the food, and such food it was, too. It's described as cuisine du terroir ; a curious notion, you might think, to serve quintessential French grub in this most English of buildings, but there you are. I am not sure what part of France chef Eric Guilbert calls home, or which restaurants he has cooked in on his way here, and neither do I care. On the evidence of lunch, he is one of the most talented and original chefs working in London at the moment.

By original, I don't mean he is ostentatiously inventive, or theatrically demonstrative. I mean simply that he produces food unlike anyone else around, food of profound deliciousness, balanced, perfectly integrated, with flavours sounding off like a chime of bells all over your mouth. There is nothing crude or obvious about each dish, nothing out of place or out of key. The plating arrangements are handsome, but not distractingly artful. Instead, there is a deceptive, artless directness.

The fair Melisande ate scallops on a bed of cabbage and pork belly with a warm balsamic dressing, and then roasted rabbit in a lavender sauce with carrots and sautéed new potatoes. I ate chilled beef pot au feu with vegetables in its jelly, then roasted freshwater eel, with leek and a Sechuan pepper sauce, finishing with and a mousse au chocolat with pistachio madeleines.

These dishes may seem a little prosaic in English, but space prevents from giving the more euphonious French menu poetry, or from enumerating all the many qualities of each dish, but here are a few to be getting on with . . .

The belly pork with scallops was crisp, fat and scorched by the touch of a grill. This served to heighten the sweetness of the scallop and cut the vegetal squelch of the cabbage.

The rabbit had been roasted to a perfect savoury sweetness, the lightly caramelised exterior breaking on to a tender, dewy interior. The sweetness was picked out by the carrots, too, with the lavender sauce rolling delicately perfumed luxuriance around them.

The earthy sweetness of the eel was cut by an unadvertised bed of braised, crushed tomatoes of fruity intensity and a dribble of herbal sauce verte as well as the exotic fragrance of the Sechuan pepper.

The chocolate mousse was a great cloud of soft richness, with tiny shards of chocolate nipping between the teeth. It comes in a bowl from which you eat as much as you can, wish or dare. My only complaint was that the bowl was stainless steel. In terms of honouring this splendid pudding, it should at least have been china.

The wine list is as individual as the cooking, and you may need to be guided through unfamiliar terrain of exclusively French vin du pays. We ended up with a bottle of Comte Peraldi from Corsica, completely unknown to me or to the fair Melisande, who is pretty expert in these matters. It completely vindicated its high price of £39.50. In fact, the whole bill came to £106.35, of which the food element was £55,50. This is a ridiculously small sum of money to spend on food which matches the magnificence of its setting