The all-white dining room of the St John era has been warmed up to look like a John Lewis 'Contemporary Dining' room set

1 Leicester Street, London WC2 (0203 696 6460)

"Useful" isn't a word you see much on restaurant websites. It doesn't quite fit with all the artfully styled food photography and action shots of chefs who fancy themselves as White Heat-era Marco. But how many of our dining choices are based, not on dazzling cooking or the lure of a shooting-star chef, but on convenience, location and user-friendliness?

Most people who ask me for recommendations in central London – and admittedly it's a self-selecting sample – aren't interested in the latest no-booking hotspot. They want somewhere handily positioned, comfortable, acoustically forgiving and not stupidly expensive. Somewhere useful, in other words.

To them, I offer Leicester House, a super-central West End restaurant which ticks the above boxes, plus one other – the food is interesting and really rather good. The location – just off Leicester Square, on the edge of Chinatown – is not short of great places to eat, or shoals of bewildered tourists to eat in them. But for the faint-hearted diner who fancies something spicy and fresh before a film or show, here's the very place: smartish, bookable and badly in need of a few customers.

The area might be seedy – Leicester House overlooks some of the last "Model Upstairs" doorways in Soho – but the building has history. For most of the last century it traded as Manzi's, a famous Italian-owned fish restaurant. Then, for most of 2011/12, it housed the ill-starred St John Hotel, one of that estimable group's very few flops. Another incarnation has since foundered, and now a group of bouncy young entrepreneurs is giving it a try, having spotted a gap in the market for French-Vietnamese food served in Chinatown by a British chef in a room modelled on a Georgian townhouse.

Visiting for lunch, I'm seated by chance at the same table which, last time I was in this room, left me showcased like a hard-to-shift window display in Amsterdam's red-light district. Thankfully, they've put up curtains now. The all-white dining room of the St John era has been warmed up to look like a John Lewis "Contemporary Dining" room set – all heritage blue-grey panelling and leather bucket chairs, with the open kitchen at one end now multi-tasking as a bar counter. They've tried hard to make the place not feel like a hotel, and succeeded – though it doesn't quite feel like a restaurant, either.

It's a slightly unlikely environment in which to experience the huge, slap-you-round-the-chops flavours of Vietnamese food. The head chef, Bruce Wilson, has no professional background in Asian cooking, but you wouldn't know it from his sure-handed, broad-minded approach. The menu brims with must-order dishes which resonate convincingly with sweet, sour and salty notes while carrying off just a touch of modern-Brit swagger.

Tender curls of robata-grilled blackened squid crown a feisty stir-fry of spring onion and samphire, shot through with just the right amount of chilli heat. Smoked beef ribs have been given a spicy rub worthy of old Soho. A green papaya, daikon and cashew salad is turbocharged with mint and the salty nip of deep-fried shallots. Scallops come with mirin-dressed seashore vegetables and a jug of bone broth: very 2015.

That broth – deep, rich and complicated – reappears loaded with crab wonton and pulled pork in what I take to be the kitchen's take on pho; the menu sticks to English wherever possible. In fact, it's hard to fathom how this is French-Vietnamese food, as opposed to, say, fusion Vietnamese, other than the brief selection of charcuterie and fromage, and an inviting Francophile wine list.

The least successful dish we try is probably the most French; beignets – flabby blobs filled with vanilla cream under a snow of shaved coconut and lime zest which come over more like Japanese pai-shu cream puffs. Much better is a dark chocolate pot, served in a coffee cup under a cappuccino froth of hazelnut cream.

A few weeks after opening, there were more punters using the doorway with the "Models" sign than there were customers in the restaurant. Lovely manager Michael, a survivor from St John days, did his best to compensate, plying us with sparkling French cider and sunny chat. I planned to return later in the week for a post-theatre bite, but when I saw Michael, poignantly silhouetted against an empty dining room, I kept walking.

It's a tricky site, but it would be a shame if this version 3.0 doesn't work. Leicester House is never going to be trendy or hot, but it's handy (another word that won't go on the website) to know of a calm, well-run restaurant in the ever-shifting confusion of Chinatown.

Vietnamese food for people who don't want to eat in a Vietnamese restaurant; surely there's a market for that? Useful, as I say. Now it just needs some customers to start using it.

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

Leicester House, 1 Leicester Street, London WC2 (0203 696 6460). Around £25-£40 per head, before wine and service