Shock and horror! French cuisine unseats the Italians as Roussillon trumps Locatelli for my favourite restaurant

I never thought I'd see this day, but I have to admit the truth: Locanda Locatelli is past its glory days.

Readers of this blog will know that the Michelin-starred restaurant near Marble Arch has long been my favourite in London, a place where the best of Italian was kicked up another level to sheer perfection. French-inspired Roussillon in Pimlico (also owner of a precious star) has, however, appeared as another frequent favourite. In the past six weeks I've dined at both, and the proximity of experiences leads me to a startling conclusion. Roussillon has maintained its excellence while Locatelli is slipping.

The service at Locatelli's is still excellent, the wine list impressive and the generous basket of Italian breads and pizze left on your table to start things off utterly delicious. The food that followed, however, was less inspiring than usual. I started with the lobster linguini. The hand-made fresh pasta was exquisite, and perfectly al dente, but the tomato sauce was too delicate and the lobster scant. This is supposed to be a hearty dish and, even when done to Michelin star standards of presentation and size, should still pack a punch of flavour. While eating it, all I could think of was how much better I remembered the same dish being at Zilli Fish (see 3.7.08). On to grilled monkfish on a bed of seaweed and rocket with giant capers and walnut sauce. The dish would have been truly great with triple the sauce. As it was, the decorative squiggle made a subtle complement to three mouthfuls of the fish, but was never enough of to deliver on the promise of a sweet and sour contrast those first tastes made.

It was dessert where things really crashed and burned. I can never resist cannoli, either in a bakery or on a menu. This Sicilian staple is the most comforting of all my childhood comfort foods. So I thought I'd see what London's finest Italian restaurant did with them. Out came a dish with two tiny pastries, about the circumference of my pinkie and no more than an inch long. I respect the idea that fine dining means delicate, small portions, but this was verging on the comic. Perhaps excusable had they been the best cannoli ever, but they were deeply average, with unremarkable filling out of proportion with the shell, so the abiding taste was of slightly over-fried pastry. Deeply, deeply disappointing, and a pale shadow of the cannoli bought for a fraction of the price at good old Missouri Baking Company on last month's visit home.

Perhaps I ordered badly. Perhaps one should stay away from things that are inspired by hearty peasant food when dining at the highest levels. But I don't think so. Locatelli's magic in the past has always been that he took the Italian basics and transformed them into something better than any memory or home attempt, seemingly beyond normal human endeavor. That magic is clearly gone. Is it, perhaps, that Giorgio himself is looking after other ventures, such as his new place in Dubai? Certainly I haven't seen him in any of my past four visits, when he used to regularly have a wander through the dining room.

And, of course, Locatelli's is expensive. Heart-stoppingly, eye-poppingly, I've-just-shot-the-entertainment-budget-for-the-month expensive. Which is OK if you're getting an exquisite meal you're going to remember all year. But three courses, all with flaws, that could be done better elsewhere? I fear Signore Locatelli will not be seeing any more of my hard-earned cash any time soon.

The team at Roussillon, however, is in for a fair chance of getting a cut of this year's bonus, be it for a simple celebratory meal or a push-the-boat-out private dinner for the wedding party after our rehearsal. (The latter depends how generous we're feeling once the rest of the wedding expenses get locked down.) My recent visit was at least my fifth, and every experience has been of equal calibre. Whether it's the go-for-broke, seven course extravaganza of the chef's menu (see 26.3.11) or a more straightforward starter-main-dessert progression, whether having a conservative couple glasses of wine or letting the sommelier roll out an indulgent procession, every experience has been to the same quality. No matter what I've had here, it's been the best I can imagine that particular dish being, served with exquisite presentation and unusual twists.

My most recent visit was no exception. The amuse bouche brought a proper twist on peasant food; essence of ratatouille in a shot glass. Surely some sort of magic is needed to take all those dark, potent flavours ... tomato, aubergine, courgette, garlic ... concentrate and retain them, and turn them into a clear liquid. Witchcraft, without doubt. One to a first course of excellent scallops perfectly grilled to bring out that hint of sweetness as the edges caramelise, accompanied by little breaded and fried parcels of ham hock. My friend's bowl of new season asparagus, picked so young and tender they looked like an alien species, was a vivid, green shout of springtime on a plate.

I moved on to the suckling pig done three ways: loin, belly and crackling. Here we had some of the world's most hearty comfort foods, retaining all their kick-you-in-the-head flavours while being presented like a work of art. The loin lean and succulent, the crackling fatty and indulgent, the belly wonderfully matched with a sweet langoustine tail that proved the argument that these are better than lobster when sourced properly. Across the table, the waitress was grating black truffle on a glistening mound of risotto, the aroma almost as good as sharing the dish.

I ended with a chocolate fondant, properly gooey in the middle and rich with the finest quality cacao. As with Locatelli's dessert, it wasn't big enough. But this time not because it was laughably undersized, but because it was the kind of sweet that tastes so good you want to keep eating long after you're stuffed. Fortunately the chef's restraint saved me from myself, and a well-judged glass of Dalmore helped all those flavours settle into a warm, contented glow of digestion.

Perhaps, as with Locatelli's, I could have ordered badly ... but got lucky. Perhaps after a few more visits I will become jaded. Anything is possible. But for now, I will shock my friends (especially you, Didier ... try not to be too smug) and bow in admiration of French cuisine. At least for now, in my experience, Roussillon is the London restaurant most worthy of your time, attention and hard-earned cash.