Dermot O'Leary has always shown great professional timing. His rise from youth TV to the shiny floors of Saturday night has been as smooth as the suits he wears on The X Factor. But as a first-time restaurateur, his timing is lousy. What bad luck to open a fish restaurant just as The End of the Line hits UK screens, the film which has taken tuna and cod off the menu for all right-thinking people.

Still, at least Fishy Fishy, the Brighton restaurant Dermot has co-founded with two old mates, tries hard to make fish-eating as righteous as possible: 99 per cent of the fish and shellfish served comes from the English Channel – some of it bought direct from local boats. Tuna and cod are not on offer – though coley, mackerel and herring are. Dermot himself is apparently a keen fisherman, so there's even a chance he'll stride up, wearing thigh-length waders, and slap something down on the table. Or was that just something I dreamt?

Like its owner, Fishy Fishy is unashamedly pitched at the mass market, but with a stylish twist. Sandwiched between Pret A Manger and LK Bennett on the edge of the Lanes, it's fronted by a large open-seating area, whose blue and white colour scheme looks spookily familiar. As does the menu, and the modernist lines of the conservatory dining area. Surely DNA tests on Fishy Fishy would uncover a genetic link to Fishworks, the once flourishing, now minnow-sized chain?

Inside, though, the restaurant has a laid-back charm which takes it out of chain territory. In a tall, narrow, Grade II-listed building, three plain, intimate dining rooms have been reconnected with their Regency past, with heritage blue walls, ivory wainscoting and some reclaimed mirrors and sea-themed paintings. Spindly wooden chairs and bare wooden tables add to the authentic look.

On a sunny weekday lunchtime, we ate in the conservatory, whose sliding windows open to let in some sea breezes. Radio 2-friendly background music, from Lily Allen to Dave Brubeck, enhances the holiday mood. Given the choice, I would probably have turned down the sound system when a live jazz band struck up in the square outside, creating a horrible cacophony, but hey, Dermot's the DJ.

The brasserie-style menu is long on choice and short on fancy cooking. There's local crab and lobster; mussels – served marinières, Provençal or Thai-style; Dorset rock oysters at a pound a pop; chargrilled mackerel with citrus butter; and a smattering of meaty and veggie options. The word "local" appears all over the menu – even attached to the calamari. Who knew there were squid in the English channel?

Compelled by some repulsion/fascination towards ordering the horribly named Brightonbaisse, I was rewarded with a well-made soup with an authentic Provençal depth of flavour. Toasted bread and ramekins of rouille, emmental, etc, were all present and correct, even if purists might argue that it wasn't a true bouillabaisse.

Other dishes were consistently good, and the fish notably fresh. Fish and chips used pollock as a very acceptable cod substitute, with impeccably crisp batter and skinny chips that had real fish shop personality. Stir-fried squid exploded in a riot of very un-local flavours, with lime, ginger and garlic battling it out with chilli heat. Grilled wild sea bass and a daily special of turbot were both simply and properly cooked, even if my guest dubbed hers Turbot O'Leary, since it looked good, but was just slightly smaller than she was expecting.

The consistency of the cooking faltered only with a pear tarte tatin, heavy of pastry and mushy of pear. "That wasn't very good," my friend said, licking her plate. With a glass of Muscadet from a short and appealing wine list priced at under £35 a bottle, we paid around £30 a head. Service started off a bit Simon Cowell, but was crisp and well-informed.

Dermot has gone on the record as saying that Fishy Fishy isn't going to be rolled out into a chain, that it's designed to be strictly coastal and local. Which is heartening to hear, from someone whose day job sees him toiling on a global TV franchise controlled by the evil emperor of brand extension. He has also said he'll occasionally be working front of house in the restaurant, which sounds like a brilliant TV format in itself.

Brighton foodies have long complained that they don't have enough decent restaurants. Fishy Fishy is a decent mid-market alternative to the existing seafood restaurants, English's and Riddle and Finns. I can imagine that its snug little dining rooms will be a really attractive prospect in winter.

As they say on The X Factor, Dermot, you're going through.

Fishy Fishy, 25 East Street, Brighton (01273 723750)

Food 3 stars
Ambience 3 stars
Service 3 stars

Around £35 a head for three courses

Tipping policy: "Fishy Fishy is the only Brighton restaurant signed up to the Fair Tips Charter. Staff keep all the tips they earn with no deductions. Discretionary service charge only applies to parties over 8; staff keep all of this too"

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