Roux at Parliament Square, RICS, Parliament Square, London SW1 (020 7334 3737). Meal for two: £150

Here, in order, are the answers to the questions I get asked most frequently about my time as a judge on the critics' rounds of the various MasterChef franchises: 1) Don't be ridiculous. That would be obscene. 2) It's a staggered start, so happily no. 3) I really don't have a clue. We only drop in for that round.* Well, I'm glad we've got that sorted.

There is, however, a bigger question that's put to me occasionally, about the impact of the show on the way food is served in British restaurants. The argument goes like this: because television is a visual medium, in which the viewer doesn't get to smell let alone taste any of the food, presentation becomes more important than it really should. At which point I should declare my love for all the MasterChefs, and not just because, from time to time, they keep me gainfully employed doing something which doesn't involve physical activity or writing. To those who whine about it I say this. It's food television. A bunch of people cook stuff and nobody dies. It's fun, compelling and beautifully edited.

All that said, I get the presentation point, especially with the professionals' show. If you don't hang about in restaurants much, you would assume from watching MasterChef, that plating up is all about thick sauces made to look like teardrops of giants with conjunctivitis with the back of a spoon, or gels dribbled from pipettes or stuff served on slates.

Each time us pampered napkin-jockeys turn up to do the critics' round we're asked what we're looking for. We always say something like: "Good taste, no self-conscious innovation, no bloody slates." We big up simplicity over complexity; in the last MasterChef pro series we all fell in love with runner-up Adam Handling's lamb dish, even though it was just meat and two veg. It didn't look like much, but God did it taste good.

And yet still the fancy plates come, and I fear it's slipping off the TV screens and on to tables in the real world. My suspicion is that, because so many millions watch and love the show, chefs and restaurateurs now think that this is the sort of presentation punters expect. Replace porcelain with slate. Smear with a spoon. Drip with a pipette. Place ingredients so they look like they were dropped from a foot above the table.

I was thinking about all this over an expensive dinner at Roux Parliament Square. This is a rare re-reviewing. I went when it first opened in 2010, when it was an edible cure for insomnia. It's located inside the Royal Institution of Chartered Surveyors, just off the square and, appropriately, I came out in love with the front elevation. There was nothing else to celebrate. It was a study in dull: dull walls, dull food, staff buffed to dull. It was an upmarket home-furnishings catalogue with canapés. Given that I'm a big fan of Michel Roux Jr, sticking the boot into one of his restaurants was not fun. His flagship, Le Gavroche, is warm, enveloping, a ludicrous indulgence of the very best kind. This was death's waiting room with gutter-to-gutter shagpile.

And then last year, a new head chef was appointed: Steve Groves, winner of MasterChef: The Professionals in 2009. Who can blame Roux Jr for using the show to find talent? I'd be lying if I claimed to recall eating Groves's food at the critics' round. It all merges into one eventually. But I did see a more recent episode where he was now leading the current crop of contestants through a punishing restaurant service. And his food didn't look at all dull. It looked colourful and bright. It looked like MasterChef. I decided to go back.

There was a temptation to narrate the food to myself as I ate, in Michel's voice, that seismic weapon which seems to start rumbling around his knees, firing off booming sentences like the thump of a timpani: "Very clean plate… lovely deep sauce… good." And a lot of it really is. There are canapés of long-braised pork, breaded and deep-fried until they become crisped pouches held together only by the action of hot fat on breadcrumb. There is whipped butter and fine sourdough bread.

A fat ravioli of crab is submerged beneath a light champagne velouté and dressed with a dribble of bisque so intense it speaks of the virtuous equation of fish shells multiplied by heat and time. This is enlightened classicism, a clear display of gastronomic literacy. The kitchen has read old recipes and knows how to turn them to the light. A single sweetbread is caramelised and served with a pile of sticky onions, crisp Alsace bacon, and a jus that is long-simmered essence of baby cow.

Goose, rarely seen on menus, arrives looking like duck's grown-up sibling, the thick breast crisp-skinned and served pink, and with a jus that tastes of the bird. Roast partridge with "haggis, neeps and tatties" reads rustic, but is something altogether more refined, the haggis arriving in light rissoles. The menu advertises Balvenie DoubleWood Whisky and here it is, courtesy of a spray. It does not add an enormous amount to the dish, but it's lovely theatre. And it all comes on black plates. Cooking doesn't get more MasterChefy than this. Or much more expensive, with starters in the teens and mains north of £20.

For dessert there is a cardamom custard tart, spiced with the lightest of hands alongside kumquat-ripple ice cream, and a banana soufflé anointed with a Valrhona chocolate sauce. You get the point. Groves really is cooking up a storm. It is not the culinary beige it once was. Appointing him was a smart move.

I just wish I could stop there, but I can't. Because while the food has changed, the restaurant hasn't. Service is desperately formal, comes with a side order of stiff, and is executed in accents so thick I had to have sentences repeated. The mood is dour, the decor still just so much sound proofing. I want to eat Groves's food, but not here, and not like this, to muted male chatter and the scrape of cutlery. MasterChef may have its presentation absurdities, but it is mostly a celebration of great food. Roux Parliament Square isn't a celebration. It's a solemn place of worship, and sadly I am not a believer.
*1) Do you really eat all that food?
2) Isn't it cold by the time it arrives?
3) Do you know who wins?

Jay's news bites

■ If you want to try other MasterChef contestants' food, there's a growing choice. Marianne Lumb, a finalist with Steve Groves in 2009, now cooks at her tiny, eponymous restaurant, Marianne, in Notting Hill, which has just 14 covers (mariannrestaurant.com). The winner in 2012, Anton Piotrowski, is still to be found at his pub, the Treby Arms at Sparkwell in Devon (trebyarms.co.uk). And the 2011 winner, Ash Mair is shortly to open a London outpost of Bilbao Berria (ashmair.com).
■ London theatreland has lost one of its own: Jimmy Hardwick, the pianist at the actors' hangout Joe Allen from its opening in 1977, has died. He was originally employed to provide the live music needed to secure a late licence, but quickly became a vital part of the place. Jimmy could segue effortlessly from whatever he was playing to the relevant tune for the West End musical star who had just walked through the door. He was still playing at Joe's until just a few weeks ago.
■ Terror in crumble land: this year's crop of much prized Timperley rhubarb is down by up to 50%, due to bad weather. Expect prices to rise.

Email Jay at jay.rayner@observer.co.uk. Follow Jay on Twitter @jayrayner1