The viewing terrace on the top, 10th floor of this new addition to Tate Modern, by the gallery’s original architects Herzog & de Meuron, is a jammy addition to London. You can climb up the grand spiral staircase, scoffing en route at the amusement-park art in the lower levels, or just be whisked up in a lift, by-passing that provocation, all for free, and get a magnificent view in every direction, surprisingly little hampered by safety fencing.

It’s a selfie paradise up there. Spread out around you is London’s morphing skyline, in which the massive classicism of St Paul’s is now dwarfed by the slippery glass erections of high finance.

It is a triumph for London that more than 100,000 people visited this new Tate Modern extension on its first two opening days alone — sad, only, that as a consequence when I visited on Brexit evening the live macaws promised in Helio Oiticica’s installation Tropicalia had defected, revolted by the sheer weight of viewer numbers.

The new Switch House restaurant, on nine, has a bar just inside the entrance where you can have a drink and, if you’re lucky, sit on one of the stools that lift you above the window-shelf to see the view. Otherwise you are going to be out of luck in this restaurant.

The surreal and dementing thing about the place is that the windows start so high up — when sitting at your table you have no view of London beneath you, and you can see only the sky and a few protruding towers. You have to get up to look down. Our waitress said, simply: “It’s designed for the staff! I think the architect forgot about the view of the people when they are eating.”

The room itself, wrapped around the core, is spacious, offering 150 covers, and pleasingly designed so that it’s nicer to be sitting with your back to the view looking in than it is facing the other way, unsuccessfully trying to look out. The truth to materials, smooth concrete and raw oak, of the building as a whole, has been sedulously maintained in the flooring and chairs and the finely figured flat oak panelling on the walls, a timber equivalent to marbling.

The best offer in this restaurant is the wine list, curated (you bet) by Hamish Anderson, Tate wine buyer and sommelier, which lives up to the reputation the original Tate restaurant list always had, while modernising the choice. There are 100 seductive bottles listed, starting at £27 but with modest mark-ups at the top end of the range. We enjoyed an organic Viognier, Domaine des Granges de Mirabel 2014, made by Chapoutier in Coteaux de l’Ardèche — not quite Condrieu but with an underlying flintiness complementing this floral grape, a bargain at £31.

The food, on the other hand, is deplorable catering college “fine dining”. It is all in-house, the work of Jeroen Schuijt, CEO, Tate Catering, Stephen Goodlad, executive chef across all four Tates, and Tony Martin, head chef.

The menu stresses creditable British provenance — Cornish red crab, Swaledale rump of lamb and so forth — to no avail. These possibly excellent ingredients do not shine, presented in over-fussy minute portions. From the starters, Cornish Blue twice-baked soufflé (£7) was a reasonably nice cheesy lump, on a few salad leaves soggy with vinaigrette, decorated with a few pointless pomegranate seeds. Chalk stream trout (£8.50) was an uninteresting pan-fried square accompanied by roasted onion slivers, white asparagus spears and a dull pea purée.

From the mains, we passed on the Smoked haddock, cockle and langoustine consommé (£18), since the waitress warned there were no cockles in it nor any replacement. Instead, line-caught wild bass, morels, green peas, English sparkling wine sauce sounded good, even at £31. It wasn’t. The tail-piece of fish was tiny but this proved not to matter, since it was fibrous and over-cooked, having apparently sat around for some time afterwards, contemplating existence, nor very fresh-tasting anyway. The sauce was a foam and just a few fragments of morel were to be found among the peas.

Portion control rules the roost here. We shared a side order of thick-cut chips (£3.50) and they were perfectly good, if modestly sized, all nine of them. Or was it eight?

Grilled Yorkshire Wolds chicken (£15) was a little better, two pieces sitting on a sticky fricassée of broad bean, pancetta and “chestnut”, the latter meaning mushrooms.

However, the puddings were nonsense. A lemon brûlée tart (£7) was fine, if not better than you could buy almost anywhere these days, but it came hideously over-decorated (“enrobed by Chef Bronwen”) with a creamy ball surmounted by a sail of lemon slice, three separate blobs of “blueberry custard”, some indecipherable “soil” element, and three half-raspberries.

Other diners seemed unimpressed too. A cogent-looking couple were seated next to us, inspected the menu, gazed around at what other people were eating, glanced at each other, and quietly left before ordering.

So this is a daft outcome for this flagship new restaurant atop a building that cost £260 million. There is clearly a problem of scale here, in delivering what at least looks superficially like “fine dining” at a non-alienating cost. But a plainer menu, simply served, would provide a better foil to the wine list.

The ground-floor bar at the Switch House does indeed have a short menu that includes rotisserie chicken but on Friday night the place was pumping out music from a soundsystem, while the tables outside were rendered untenable by a vortex of wind. Tate Modern provides premier promenading, to be sure, but perhaps just drink here and eat elsewhere? Particularly as those vaunted “panoramic views” are so tauntingly cut off the moment you sit down.

Open Sun-Thurs 11am-4pm, Fri-Sat 11.30am-10pm. A meal for two with wine, about £100-£120.

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