What do you want from your friendly neighbourhood gastropub? Striking the right balance between pub and gastro is a tricky business, like getting the correct proportions of gin and Cointreau in a White Lady. You can't afford to dispense entirely with the pints-and-pork-scratchings, pubby stuff, or your inherited clientele will totter uncertainly off elsewhere. But if you start offering pub customers "confit leg of venison" in a "star anise jus" for £13.50, you've got to ensure the quality matches the pretension.

The Avalon used to be The George, a spectacularly grotty pub in that featureless territory between Clapham South and Balham. It's had one hell of a makeover. The new owners, Tom Peake, Mark Reynolds and Nick Fox, a trio of entrepreneurs who display a touching faith in south London (they're responsible for the Bolingbroke in Battersea, the White Hart in Kennington and two fancy pubs in Clapham, the Abbeville and the Stonhouse) have gone for high style throughout.

From outside it looks gorgeous, light bursting out of four bay windows. The name "Avalon" refers to the mythical "apple island" where King Arthur was buried, but is also fatally redolent of a soporific Bryan Ferry album. The walnut bar with its handsome copper lamps serves mostly lager, and punters chat across high wooden tables that seem to insist you sit up straight and don't slouch. The lounge area offers comfy dark leather sofas and a mural that looks like several pre-Raphaelite paintings run together. This is not a place where geezers, Herberts and street traders would feel at home. You can't imagine Chas'n'Dave getting far starting a knees-up in this chi-chi boozer.

The dining area is sensational: a cavernous room, designed with terrific flair, dominated by two chandeliers made from chain links and metal offcuts from naval ships. The walls are lined with white tiles in the manner of a civic lavabo, but not unpleasantly so; and at the end a 15-foot-wide mirror is split into 36 rectangles like mullioned windows. I thought the lighting unnecessarily harsh, but the place was gratifyingly full for a Tuesday night. Word has clearly spread since it opened in November. You can tell when local punters are willing a new place to succeed: there's a buzz of conviviality that says people are anxious to claim it as their own.

It's just a shame the food isn't terribly good. The dinner menu is long and appealing, but unimaginative: steaks and pies, mussels, potted crab, smoked halibut, slow-cooked pork and lamb, confits of duck and venison – jolly nice, worthwhile, February-evening-comfort-food stuff, but just a teeny bit Snoresville. My seared scallops with crispy black pudding were served warm (and not crispy) while an accompanying "spiced Jerusalem artichoke purée" was wholly characterless (and unspiced). My pal Tim judged his foie gras terrine insufficiently thawed – "Foie gras isn't supposed to be al dente, is it?" he asked – but admitted that, once thawed, it played nicely with a coarse fig chutney.

Tim's main course of whole boneless sea bass with a confit of fennel was more successful – the fish perfectly cooked, the fennel stuffed inside it, and the flavours triumphantly entwined. My 10-hour slow-cooked shoulder of lamb was as fibrous and gelatinous as a shank, but it was clearly overcooked. There's a difference between slow-cooked and over-cooked, and the wholesale lack of succulence suggested the latter.

How come it was square? The waiter explained that several lamb shoulders are cooked simultaneously, the flesh removed and pressed together in a roasting dish, then finished and cut into squares. Heaven protect my sensitive soul, but it seemed to me an excessively industrial way of preparing lamb. An anchovy and caper sauce lay on the plate as if it had nothing to do with the meat it surrounded.

The chef here, Marez Loukal, previously worked at Chez Bruce and Quaglino's, an excellent twin pedigree. Would Chez Bruce have dished up lamb like this? Was Mr Loukal trying to cook too many bog-standard dishes for too many Claphamites? Or just having an off day?

Puddings were fine, the lemon meringue pie just right texture-wise. My banana tatin had been sitting in the oven maybe half an hour too long, but was hot and sticky and very welcome before we plunged out into the frozen night.

It wasn't a disastrous dinner, just frustratingly ordinary. When a pub has been so expensively kicked into gastropub league, the cooking should be handled with more style and conviction than The Avalon can currently muster. But I'll be back in the summer and will be amazed if the food in this charming place isn't attracting four-star compliments by then.

The Avalon, 16 Balham Hill, London SW12 (020-8675 8613)

Food 2 stars
Ambience 3 stars
Service 3 stars

About £100 for two, with wine

Tipping policy: "Monday-Friday lunch, no service charge; 12.5 per cent optional service charge the remainder of the time, of which 100 per cent goes to the staff; all tips go to the staff"

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