Just how grand can gastropubs get? They’ve climbed an awful long way since The Eagle in Farringdon Road pioneered the concept back at the start of the Nineties and they are still effortfully mounting ever higher.

One of the swellest of the past few years has been the Thomas Cubitt in Elizabeth Street, which likes to emphasise its affinity with Belgravia rather than mucky Victoria. Now the owners have opened a second place, this time indisputably in the heart of Knightsbridge, in Motcomb Street. To walk down here is to think of Philip Larkin’s line: “I listen to money singing.” Bentleys are commonplace, only the Maybachs turn heads.

The Panthechnicon Rooms calls itself a bar and restaurant, disdaining the very name of pub, and boasts a little of its location. Just as the Cubitt references the great architect, the Pantechnicon is named after art storage rooms that dominated Motcomb Street until destroyed by fire in 1874. (The surviving façade down the street, currently under scaffolding, now houses a Starbucks.)

The restaurant upstairs is frankly luxurious. The room is interestingly and beautifully decorated in the sober Gustavian manner that works so well in the Cubitt: the frames of the fine sash windows are painted matt greeny-black and billow with linen curtains; there are substantial leather chairs and lots of space for the tables. Once some intrusive music has been turned down, the atmosphere is calm and restorative.

The menu, too, is at once lavish and plain, opening with three kinds of oysters, followed by three kinds of caviar, from 30g of farmed from Aquitaine at £60 to 50g of Beluga at £295 (not a mis-print, I’m afraid). There’s lots of lobster, four choices of smoked and cured fish and plenty of pricey basics such as whole grilled Dover sole with lemon and watercress at £27.

Lobster salad and parsnip crisps was quite a small starter for £16: some nice discs of fresh-tasting lobster, plus a claw, lurked beneath a mound of salad, a bit overpowered by the crunchy strips of parsnip. Twice-baked stilton soufflé, with a walnut and apple salad (£6.50), was the only disappointment. Although it tasted nicely enough of eggs and cheese, the texture was wrong: collapsed and clammy, without the benefit of any crusting from the second baking either. It’s an easy enough dish to get right — and this one was no match for Rowley Leigh’s twice-baked goat’s cheese soufflés, such a treat in the old days at Kensington Place.

“Rose veal, green beans & salsa verde” (£14.50) was the cryptic description of what turned out to be a delicious, crisply breadcrumbed classic Wiener schnitzel, accompanied by a nice potato mash and green beans, topped with a basil pesto, freshly made but hardly necessary when a mere dash of lemon juice would have lifted it better.

Seared tuna fillet (£19.50) came as a thick chunk, nicely rare on the inside, served with a construction of mixed green and white asparagus spears, and some well softened and crisped fennel. A side dish of samphire (£4.50) had been steamed and, while just the right texture, it had stayed intensely salty compared to samphire that’s been boiled, however briefly.

All of this was easy to enjoy, elegant food for the well-fed rather than the hearty fare of lamb shanks and sausages that keeps more humdrum gastros in business. A dark chocolate marquise with honeycomb and pistachio ice-cream (£7.50) was sensationally good, too, both refined and deep in taste.

Service is friendly and attentive, tap water is assiduously offered and the wine list is highly inviting if you don’t look meanly at the prices. A glass of aromatic Argentian viognier is £4.50, an excellent Brouilly £7.50 — and the bottles are carefully brought to the table to be poured. Later on, there’s a section called Icons offering dreamy bottles at prices one expects to pay for a fort-night’s holiday.

It’s only the price that’s not to like about The Pantechnicon Rooms. It’s not much cheaper in the bar downstairs and the tables outside either. An almost identical menu is served, with starters slyly renamed “small plates”, puddings a pound cheaper and some economical substitutions made (plaice and chips with mushy peas at £11.50 standing in for the Dover sole, for example). But you might as well go the whole hog in the comfy chairs upstairs.

About the cheapest lunch possible here would be smoked haddock and salmon pie at £8.50: little chunks of fish in a runny bechamel, beneath nicely parmesan-crusted mash, served quite plain in a cast-iron gratin dish. With service and a glass of verdicchio, very enjoyable on a sunny pavement, this still comes out at £16.88. But for Knightsbridge, money central, that’s almost a snip.