Flat Three, restaurant review: 'Hardcore food spods should be all of a flutter but the rapture never happens for us'

It was the £6 glass of green tea that power-drilled the coffin lid shut on any last flickerings of good feeling I had about this week's restaurant. Six pounds! For an inch of brackish warm water infused with a few plant buds. It would have been the last straw, had Flat Three not been the kind of place to have already taken the last straw, burnt and freeze-dried it, and served it crumbled over a pickled sea urchin.

Born of an experimental supperclub collaboration which matured into a real-life restaurant, Flat Three's none-more-foodie concept is a mash-up of Japanese, Nordic and Korean influences, helter-skeltering across continents with an open mind and brimming foraging bag. Head chef and co-founder Pavel Kanja, an alumnus of Scott Hallsworth's Wabi, does things the hard way; his menu is spiky with charred fish bones and rape- leaf water kimchee. A typical dish reads "alkaline udon, lemon thyme, onsen quail egg, baked salt koji, sea urchin butter".

It's the kind of fetishistic whimsy guaranteed to set hardcore food spods all of a flutter, not to mention critics in search of something new to write about. But – and it's a big but – things are different round these parts, a mansion-tax-ready corner of west London not famous for the diversity of its restaurants. Holland Park is surprisingly short of interesting places to eat, considering its super-rich residents, who include Gary Barlow and Simon Cowell (not in the same house). The idea of launching an expensive, ambitious Japanese-ish restaurant here is not a totally daft one: the locals are cosmopolitan and carb-averse. But it's risky.

The site, unpromisingly located in a basement below the main shopping strip, is surprisingly airy and elegant. But it's immediately clear the place suffers from an identity crisis. In an open kitchen, we see bearded and tatted chefs labouring intently over foraged morsels: so far, so London 2015. But the platoon of burnished, high-beam robo-hostesses who take over belong in another restaurant entirely, one serving hand-massaged wagyu fillet to visiting non-doms.

On a less than busy night, the room is as hushed and tiptoey as a temple and, at first, we're prepared to be converted. But the rapture never happens. The £49 five-course "chef's choice" menu (seemingly the cheapest way to go) is a chimera of vanishing textures and challenging, almost-nice flavours, as insubstantial as a bonito flake which curls up and vanishes on the tongue.

The pattern is established with the first dish, which muddles the brisk asperity of shaved raw turnip with crumbs of "crunchy milk", as sweet and malty as Ovaltine. Three stamp-sized lozenges of belly tuna come with a trout-bone ponzu and fermented soya beans crumbled into a pungent, feculent dust.

A single scallop, meltingly caramelised, gets the Scandi-Asian treatment, with a feathery frill of kombu (pickled kale), a pool of buttermilk and some kind of salty pollen. "Did you enjoy your fish bones?" asks our waitress as she clears. At which point I make a note not to come back with the kids.

Some dishes seem to be put together conceptually, rather than for pleasure; why else partner a crisp-skinned tranche of lightly smoked salmon with a swampy mulch of green-tea leaves? And the modernist, miniaturist approach requires perfection. When you're only getting four bites of lamb, albeit draped in chrysanthemum leaves and served with charred mustard-leaf piccalilli, one of those bites shouldn't consist entirely of fat.

"I'm so hungry," groans my guest after four courses, plus a starter we're encouraged to order, even though we've already chosen the five-course tasting menu. Not the only bit of upselling from a waitress who seems to be working from a prepared script, and steers us relentlessly up the list when we attempt to order one of the few wines costing less than £40. And those enraging £6 green teas were her suggestion.

All the Michelin-friendly frottage, the fervid introductions of new dishes as "a brilliant idea from the chef", the donning of a single white glove, Michael Jackson-style, to clear our plates, makes for a claustrophobic night. And the featherweight poshness just doesn't chime with the let's-char-the-fishbones-right-here spirit of the food. It's like we've fallen into a wormhole somewhere between Hackney and Gordon Ramsay.

None of which would matter if we'd been knocked out by the food. But I'm afraid we just weren't. Some of London's most exciting restaurants, notably the Clove Club, have grown from supperclubs. But in the case of Flat Three, the transition just hasn't worked. The founders have tried to preserve the down-home spirit by naming the restaurant after the address in which the venture started. So in the same spirit, I'll stick to it for my star ratings. A flat three.

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

Flat Three, 120 Holland Park Avenue, London W11 (020-7792 8987). A la carte around £50 a head before wine/service. Tasting menus £49 (five course) or £79 (nine course)