Mayfair has developed, perhaps even cultivated, a reputation for joyless excess, epitomised by its surfeit of characterless bars charging £20 for a second-rate cocktail and a first-rate scowl.

See related David Shrigley on Sketch

Sketch is the precise opposite of that. Sitting hard up against the border with Soho, it represents something of a challenge to its hipper, more creative neighbour.

From the pavement, only a peachy glow in the upstairs window hints at what lies behind the sobre Georgian facade. To wit: a green-lit forest glade, a pale pink diner, a bar masquerading as a futuristic space pod and a high-ceilinged amalgam of neoclassical architecture, art deco decals and Japanese lanterns, resplendent against a backdrop of red velvet and orange wallpaper.

Where to begin? Perhaps The Parlour, which breaks you in gently with a relatively conventional bar. Relatively: the 18th-century cornices are touched with neon and its luridly upholstered chairs sport legs in the form of ballet shoes en pointe. Self-identifying as an “eccentric patisserie”, it serves hearty breakfasts and brunches until the 5pm witching hour, which heralds the arrival of cocktails and bar snacks.

The Glade, one step further down the rabbit hole, serves the same menu in a tree-lined grove. Not a real one, of course - the mirrored tabletops and velvet-clad chairs give the game away - but a fantastical, fairy-tale replica. I half-expect an impromptu performance of A Midsummer Night’s Dream.

Before one can begin, we ascend to The Lecture Room and Library, Sketch’s two-Michelin-star restaurant. The entrance is nothing if not theatrical: a grand, red-carpeted staircase leading to a dark anteroom, from which we emerge through a pair of double-height doors, opened simultaneously by waitresses in white dresses.

The service is impeccable all evening. Well-drilled yet by no means robotic, it is delivered by personalities ranging from the reserved to the relaxed. The sommelier counsels us with an old-school conspiratorial intimacy, proposing a glass of champagne to get things going, before furnishing us with a white Saint-Aubin Premier Cru, generous and ripe with a spine of steel, and then a red Bordeaux from Chateau Alta Gaia for the meatier stretch of the menu.

Like the room in which it’s served, the food draws from an eclectic palette. France and Italy are well represented, especially in the lamb dish, which consists of a deeply flavoured saddle and a bite-sized rack alla Milanese - a crisp lollipop of meat, breadcrumbed and fried - along with spring onion, oregano and pommes Maxime’s (potatoes sliced, roasted and named after a restaurant in Paris).

Home-made tagliolini, however, gets a piquant Russian kick from a jewelled cluster of Ossetra caviar, and an oyster with black truffle derives additional earthiness from a spoonful of Guinness foam, applied at the table from the head of a pint. Green mango and blood orange add a Thai-tropical flavour to the lobster dish that follows.

But stout spume notwithstanding, there are few gimmicks here - just confident cooking and a willingness to push the envelope.

Perhaps a little too far, in one or two cases. I baulked at the saffron in the first of many puddings - too strident, too savoury - but a more conservative confection of hazelnut cream won me back, and the cumin-infused mousse of the third (or possibly fourth) dessert was the right side of adventurous - adding depth and warmth without shouting about it.

At £120 a head for the food alone, the prices are pure Mayfair, but that buys seven official courses, plus amuses bouches aplenty (which are indeed amusing, especially a delicate langoustine reclining in lobster bisque).

And the toilets alone must be worth at least £20. The glittering black-marble vault of a bathroom halfway up the main staircase is closer to the dining room, but take a walk to the other end of the building, through the pink fever dream of the The Gallery, its walls lined with 91 artworks by David Shrigley, and around the space-age East Bar, to where giant futuristic eggs conceal the necessary conveniences.

Then step back onto the pavement, where normal service will be resumed.

The Lecture Room and Library at Sketch, London W1: sketch.london