The demise of London’s Chinatown has long been predicted, what with recent rent and rate rises, and diners’ changing tastes.Yet on a spring lunchtime last week, business on Wardour Street was booming, with alfresco noodle-slurping, long queues and endless selfie sessions all in full swing.Song He Lou, a historic restaurant brand that champions Suzhou cuisine, clearly believes there are big profits to be made in this postcode, and it has put its money where its mouth is by opening a whopping 144-seater right here in the centre of Chinatown.I’m not chucking in that “historic” willy-nilly, either: Song He Lou was founded in Suzhou near Shanghai almost 270 years ago, during the reign of Emperor Qianglong, and makes Rules in nearby Covent Garden, which is a piffling 227, look like a fly-by-night pop-up.After the best part of three centuries in China, this new London branch is Song He Lou’s first overseas flagship.

And, despite its size, it feels oddly low-key, too: there’s no neon, no bunting and not much jostling for tourist dollars at all.Well done if you can find it without wandering past the rather understated brown frontage and discreet name sign at least twice.Inside, it’s all grey stone and bamboo lightshades, and you’ll only by accident, if at all, learn that this place is a big deal in China.With three floors to fill, that feels a rather bold approach.There are none of those “Here’s the story so far …” posters, complete with maps and company messaging, that you might expect from an ancient brand, though there are two small nods to quirkiness in the form of cute little chairs with pull-up lids you can hide your handbag inside, then shut and sit on, like a giant goose; and the wonderfully loud soundscape of Suzhou Pingtan, or operatic folk tales, accompanied by a three-string Chinese lute.

The staff, who are absolutely delightful, sensing my less-than-amateur-level hold on Jiangnan culture, found me a photograph online of said instrument and provided a brief running commentary on the love, loss and family drama being crooned about.Song He Lu’s most celebrated dish is its soup noodles in broth, which come with the likes of sweet-and-sour “squirrel-shaped” bass, sizzling eel, braised pork and a gloopily delicious soup of crabmeat with roe.The menu offers about half a dozen rather sizeable set-meal noodles, including various seasonal vegetable sides, vinegars and shredded ginger.There are further sides on offer, among them thickly battered pork loin, mustard greens with bamboo shoots, wobbly plates of sliced stir-fried kidney and even just a pair of fried eggs; there are preserves of candied kumquats, crushed olives and dried bamboo shoots, too.Jiangnan cuisine has been dubbed China’s best-kept secret, and I wonder if Song He Lou’s rather subtle and reserved nature means that will endure.

Westerners who have found the rise of, say, Xi’an cuisine across the UK thrilling, thanks in no small part to its blistering chilli heat, the girth of the noodles and the sheer abundance of alliums, may well find the food of Souzhou a little elegant and aloof by comparison.Song He Lou’s pale, wispy noodles come folded into neat bundles, submerged in a bowl of comforting yet unobtrusive chicken-based stock and enlivened with the merest scattering of finely chopped spring onion.They feel less bolshie and showstopping than somewhat medicinal, non-wasteful and humble.I drank a jasmine silver needle tea served from a dinky little blue pot, and ordered the squirrel-shaped fish out of sheer curiosity.It turned out to be a whole small bass, filleted, then scored across the flesh in criss-crosses, so that, after it’s been dipped in flour and deep-fried, it turns fluffy and layered and looks a bit like a squirrel’s tail.

The fillets are served with the fish’s head returned to its rightful place, all covered in a vivid red, vinegary and rather sweet sauce that’s offset by a side of bitter mustard greens, dark, sticky preserved mushrooms and some not-particularly-pickled cucumber.The portions are plentiful – I ordered for one and it could easily have fed three – but somehow I still bravely found room to face Song He Lou’s gelatinous, red bean paste-based desserts, all of which are the epitome of stickiness and have the texture of particularly tasty Silly Putty.They’re not enormously sweet, either, and the three-colour rice cake, especially, has a lovely, rose fragrance.Song He Lou isn’t remotely raucous or overwhelming; in fact, it feels oddly maternal, and perfect for a solo lunch or a place to hide from the perma-hubbub of Chinatown outside.Order some tea, enjoy the comforting noodles and leave the rumpus behind.

Song He Lou 22 Wardour Street, London W1, 020-4531 2678.Open all week, noon-10pm (11pm Fri & Sat).From about £30 a head, plus drinks and service