Rock Salt, 4-5 Fish Market, Folkestone, Kent

Can ex-Ramsay chef Mark Sargeant make Folkestone a foodie destination?

If you've glanced straight at the score for this restaurant, let me explain. The food at Rocksalt scores a straight eight. It's excellent: fresh, imaginative and very, very well cooked. But the service is woeful: I mean properly bad.

And it all started so well.

I'm partial to the south-east coast – my friends Ann and Rick live in Broadstairs, Sally is down the road in St Leonards and Whitstable is Clerkenwell-on-Sea, it seems. Now Folkestone is getting a bit of big-city zhoozsh in the form of Mark Sargeant, another of those ex-Gordon Ramsay chefs making a noise on his own. Rocksalt is the first of his two projects in the town; the other – Smokehouse fish and chips – is coming soon.

So a weekend jaunt down to Folkestone it is. A stroll along the front to the harbour, bathed in sunshine, builds the appetite and the expectation – the dark-wood-clad building, with its sleek title picked out in white, can be seen from some distance.

The austere entrance is guarded by a Bond villain straight out of central casting. He makes sure we're not unexpected (Rocksalt is a hot ticket just a week in), then we have the big reveal – through a doorway into a curved room, of which one side is completely glass, with views over the harbour and sea beyond.

Folkestone is hardly St Trop, but the view is charming. A narrow strip of terrace would be delightful to sit out at during daytime; inside, the blond-wood parquet floor and dark-wood modern tables and leather-cushioned chairs are very modish.

Miss T asks for cherry Coke. The waitress says no but then, moments later, brings normal Coke and a saucer with three plump cherries, which is thoughtful and fun. Like I said, it started so well.

We nibble on some Kentish sourdough bread with Rocksalt taramasalata for £1.50. It's very good indeed, pale-pink, tangy and rich, and sets us up for starters proper: a tankard of grilled prawns, potted crayfish tails, fish soup and dressed crab with harissa and toast (all around £7.50). The generous shell-load of mildly spiced crab is my favourite, but the more poky crayfish ensemble is a close second. And the soup is the real deal: rusty orange with dense, shellfishy flavours. I consider a prawn but the tankard (it's a half-pint) is already empty and P is holding his greasy, shrapnel-flecked hands aloft. There's no finger bowl. We flag down a waiter. "Uh, sorry, I should have brought one."

The debris of the starters remains in front of us for 10 minutes. No biggie, since we're people- and seagull-watching and anticipating the arrival of duck-fat chips. A word about the menu: Rocksalt is very keenly priced. All sides are £2.50 and only the catch of the day is north of £15. This is sensible – Folkestone doesn't have quite the allure of, say, Southwold, so much of the clientele will be local – who should expect value for money.

Here, they definitely get it – on the plates at least. My main, today's catch of Dover sole with asparagus and sauté potatoes, is wonderful – a good-sized fish, buttery without and soft inside, with lovely seasoning. Mr M's special, sea bream, comes with samphire, crushed potatoes and coriander pesto. The fish is fabulous – meaty and generous, although the seasoning's on the mild side. The kiddos make short work of squid with lime and chilli, and lemon-sole fingers with mushy peas: from my forkful, both are very good examples of their genres.

This time the plates linger even longer – not ideal in any circs, but with fishy scraps it quickly becomes unpleasant. A waiter drifts over thrice, only to show a couple to a nearby (uncleared) table and take the bill to another couple. Is it just that we're at one end of the long room?

From a 7.30pm start, we finally get puds at 9.45pm, when the children are flagging. Excellent pavlova, chunky Bakewell tart and an imaginative cold chocolate and sea-buckthorn fondant give us enough energy to propel us back to our B&B.

If Rocksalt is to work, Mark Sargeant needs to fix the service, and fast. He's not in tonight, I'm told. He's not cheffing here at all, in fact – Simon Dyer is, and he's very good. The dozy staff forgot to put our two mains on the bill – which I only notice a day later. I've contacted Mr Sargeant as I really want this place to succeed. The sweet lady in my B&B was so excited about a smart new restaurant in town. Rocksalt's got pulling power, but it's going to take more than sourdough and salmon to keep people coming back.

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6.5/10

Scores: 1-3 stay home and cook, 4 needs help, 5 does the job, 6 flashes of promise, 7 good, 8 special, can't wait to go back, 9-10 as good as it gets

Rocksalt 4-5 Fish Market, Folkestone, Kent, tel: 01303 884 633 Lunch, daily. Dinner, Mon-Sat. About £100 for two, with wine

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Reviews extracted from 'Harden's London and UK Restaurant Guides 2011' www.hardens.com