Northbank, One Paul's Walk, London

Perfect riverside location, warm and friendly welcome... there's only one thing missing at London's Northbank

If a restaurateur takes a night off, even the most obtuse diner often picks up that something is missing. The warmth of greeting, the smoothness of service, perhaps the pacing of the meal – something is not quite right. But if the chef takes the night off, how do you know? I've had some of my best meals on the chef's night off.

At the relatively new Northbank, tucked under the Millennium Bridge, restaurant manager turned restaurateur Christian Butler is very much on the case. He meets, greets, collects coats, decides whether you are booth-worthy, takes drink orders and is an extremely affable host – an especial rarity in the City, where most restaurants belong to chains.

In the kitchen, I assume, is Peter Woods, previously of Allium and The Belvedere, who has collected some enthusiastic reviews since opening late last year.

It's a great little spot, with a long bank of windows opening on to a riverside terrace that's just busting for summer to come along. On this wintry night, it has a moody NY-Lon cocktail-bar buzz, with its low-key lighting, smoked mirrors, dark-green leather banquettes and filmy organza curtains. Look again, and you see cute little booths for two (perfect for St Val's) and subversive wallpaper from Timorous Beasties that looks like an 18th-century toile de jouy design but is delightfully frank in its illustrations of city life.

The menu has a charming West Country bias, due to Butler's Cornwall upbringing, with its hog's pudding (a sort of West Country haggis), Falmouth crab with clotted cream tart, Duchy of Cornwall oysters, grilled Red Devon steak and chips, and a "cream tea Martini" for pud. It's a smart move, as we all have a tender spot for the good food of the south-west.

West Country meets French bistro in a starter of steamed mussels with cider and bacon (£7), which lurks in the bottom of an enormous black enamel mussel pot like a rockpool. It works well, the juices being lightly velvety without being overly rich and creamy, and the mussels sensitively cooked, removed from the heat as soon as their shells open.

Devilled kidneys on toast (£6.50) is the perfect starter for someone who had said not hours earlier she was craving kidneys on toast. It's simple, saucy and spicy, with a thatch of fresh leaves on top.

So far, so good, although the nice-as-pie floor staff seem a bit ditzy, taking orders to the wrong tables and not being there when needed. When the inter-course pause lengthens into a delay, I begin to wonder if the head chef is in. When the lamb stew with herb dumplings (£14) arrives, I rather hope he isn't. Stringy, over-cooked lamb and gluey, heavy dumplings do not a blissful meal make. Likewise, pheasant breast (£15) is dry and boring, served with a toffee-sweet braise of red cabbage.

The wine list is top-heavy for such a commercially savvy menu, and needs more options – like the crisp 2006 Lois Gruner Veltliner for £22.50 – under the £30 watermark. A 2002 Ata Rangi Crimson, a "young vines" pinot noir from New Zealand's Martinborough region (£43), is ripe and juicy, but lacks any real depth.

There are stock standard pear and blackberry crumble and warm apple tatin offerings for dessert, but by now, I suspect they could be over-baked. The cream tea Martini (£7.50) comes with toy scones and clotted cream. Cute, but the scones shatter in the mouth from, yes, over-baking.

This is a smart, chic place with a good heart and a lot of good ideas, seemingly right for its City trader/Tate Modernite crowd. And yes, I discover I am there on the chef's night off. Let us assume it gets incrementally better with the head chef on, or why the good reviews? Besides, I can hardly complain about a chef having the night off when I do it myself every time I go out for dinner instead of cooking at home.

13/20

SCORES: 1-9 STAY HOME AND COOK, 10-11 NEEDS HELP, 12 OK, 13 PLEASANT ENOUGH, 14 GOOD, 15 VERY GOOD, 16 CAPABLE OF GREATNESS, 17 SPECIAL, CAN'T WAIT TO GO BACK, 18 HIGHLY HONOURABLE, 19 UNIQUE AND MEMORABLE, 20 AS GOOD AS IT GETS

Northbank, One Paul's Walk, London EC4, tel: 020 7329 9299. Lunch daily; dinner Mon-Sat. Around £110 for two, including wine and service.

Second helpings: More bridge-side bistros

The Old Bridge Hotel

1 High Street, Huntingdon, Cambridgeshire, tel: 01480 424 300

Located next to an imposing medieval bridge, this ivy-clad hotel is known for its award-winning wine list and accomplished Modern British cooking

The Bell at Skenfrith

Skenfrith, Monmouthshire, tel: 01600 750 235

An idyllic restaurant with rooms situated beside an historic arched stone bridge straddling the River Morrow, known for its trout fishing

Blueprint Café

Design Museum, 28 Shad Thames, London SE1, tel: 020 7378 7031

A popular Thameside restaurant with two major drawcards: Jeremy Lee's solid, finely honed British cooking and gasp-inducing views of Tower Bridge