The Fenchurch Seafood Bar and Grill, restaurant review: Lunch in the Walkie Talkie isn't a patch on the vertiginous thrill of the Shard

I've reviewed plenty of unpopular chefs over the years; bully boys, telly hustlers, domestic monsters. But this is the first time I've eaten in a truly unpopular building. Namely, 20 Fenchurch St, aka the Walkie Talkie, that swollen, top-heavy skyscraper which looms boorishly over the City, endearing itself to neighbours by beaming down a death ray of refracted sunlight from its concave surface, causing cars to spontaneously combust. As a symbol of laissez-faire capitalism, it's The Shard with added Emperor Zurg.

In the most egregious attempt to 'give something back' since It's a Royal Knockout, the building's owners have opened its upper floors to the public and called them a Sky Garden. Anyone can visit, provided they have a reservation at one of the two restaurants, or have pre-registered online. At entrance level, there's airport-style security, with coats and bags handed over for screening. Then it's up, up and away to the 35th floor, to emerge, wide-eyed, into the cavernous Sky Pod Bar.

Seemingly suspended in space, it's a triple-height glass atrium so huge that the puny earthlings scattered around look minuscule. The 360˚ views are epic, but it's freezing. In the summer, though, it will be a fantastic place to come for a drink, safe from any rogue death rays bouncing around at ground level.

One level higher, and reached via a wide staircase through a sub-tropical garden, is The Fenchurch Seafood Bar and Grill, the Walkie Talkie's Finie Dinie restaurant. Climbing through the vegetation into the glassed-in interzone which houses the restaurant feels like penetrating the inner lair of a Bond villain's fortress. Only a Bond villain's doors wouldn't glide open to envelop you in a powerful whiff of school dinners.

A snagging problem, clearly. Otherwise, the dining room is pristine, in a posh hotel-ish way, spiffed up in luxe shades of black, brown and gold. Weirdly there isn't much of a view, on a grey lunchtime, even from our window table, which looks out over the Sky Garden rather than the skyscape beyond. There's none of the vertiginous thrill you get when eating window-side at the Shard. As my guest observes, we're in the garden shed of the Sky Garden.

Nor does the menu promise much in the way of thrills; padded with plutocrat-pleasers like Oscietra caviar, lobster cocktail, grilled foie gras and Chateaubriand (£76 for two to share), it apparently isn't trying to match the innovation of the architecture. But the bread is fantastic, particularly a pillowy focaccia humming with rosemary, and the flavour-bomb amuse – some kind of crisped fish skin - sets the stage for a surprisingly good lunch.

Take the scallop starter, which reads School-of-Conran dull, but sparkles; the seared scallops paired with pork cheek braised to a high shine, and complicated with a garnish of monks beard, samphire and shaved fennel.

Mackerel escabeche comes with an even more exotic array of fiddly, on-trend fixings, making every mouthful pop.

A main course special of pheasant, the breast roasted, the leg confited and shredded through a nubbly barley risotto, is galvanised by crisp bites of dehydrated kale, and swoony heritage carrots. This kitchen is really good with veg, using it to do interesting things around the edges of a straight menu. Rib-eye steak is served more simply, with a jug of irresistible marrowbone gravy, and is blandly succulent, to suit the business diner who doesn't want to waste too much time chewing.

The finesse continues with desserts, a pert rhubarb soufflé and an oozy slab of caramelised quince with macadamia crumble, unexpectedly adorned with fronds of fennel leaf.

The inventiveness of the cooking doesn't quite fit with the bland smoothness of the ambience; with its dinner jazz, big white plates and ultra-attentive service, we feel like we've fallen through a wormhole back to the mid-Nineties. Maybe the room works better at night, but at lunchtime, it lacks the drama and magic you'd expect from the sky-high location. The prices certainly match, though; with a single glass of wine each, our bill climbs to £80 a head faster than the lift reaches the 35th floor.

The only really exciting moment comes when the glass-box private room suddenly turns opaque, sealing off its occupants at the touch of a button. Quite why they've come to the top of a skyscraper to sit in a viewless box sealed within another box is a puzzle. The Darwin brasserie one level down looks a bit more fun, though again, it's rather sealed off from the views.

The developers could have done something exhilarating with this vast expanse of air and light; they surely would have done in Paris or New York. Instead, they've gone for by-the-book corporate smoothery. The big, bad building that melted London may swagger like a central-casting villain, but inside, it feels about as risky and thrilling as Center Parcs.

Food ****
Ambience **
Service ****

Fenchurch Street, London, EC3. Around £65 a heard for two, including wine. http://skygarden.london/fenchurch