All us critics have little things. Little things we do, peculiar specialities, personal critical G-spots. For some, it’s the bread that’s the bellwether; for Michael Winner, it’s the size of his table and his orange juice. I’ve known food critics who can become puce over settings, butter dishes and steak knives. I know one who orders things that aren’t on the menu. And there was said to be a memorable, possibly apocryphal, Australian critic who specialised in creating catastrophes. He’d bring his own cockroaches and dog turds. He’d be sick on the reservations book, and gave a particularly gothic epileptic fit. Legend has it that he was finally moved to provincial theatre after an altercation with a flambé trolley that left a lady diner entirely bald and a wine waiter naked.

These are the small, arbitrary divining rods critics whittle for themselves, and I try not to have any. I want to go to every meal as if it were my first — or last. But I’m a creature of habit (I wish I could still add “all of them bad”, but now they’re mostly just boringly repetitive), and there are things that always snag me.

Like deer. If there’s venison on the menu, I have to ask what sort. Do you know how many species of deer are wild in this country? Neither do I, but they range from muntjak, the size of a wet poodle, to red, which is like a small horse. They’re all very different. Restaurants wouldn’t write antelope on their menus: they’d specify springbok or kudu. So why not deer? By the way, do you know the defining difference between deer and antelope? It’s the horns. Deer shed, ’lope don’t.

Anyway, I was in Pétrus and there was venison on the menu. So I ask the waiter what sort. “It’s deer.” What sort of deer? “It’s young deer.” No, what sort of young deer? He begins to look around, with the first swell of panic. “It’s young, wild, happy deer.” No, what... “Look, I’ll go and ask.” He scurries off to the kitchen, and I’ll bet a fallow to a wapiti that Marcus Wareing’s saying: “Shit, we’ve got that bloody AA Gill in.”

The thing is, I know the answer: it’s roe. It’s always roe — saddle of roe. I just have this nerdy, trainspotterish need to quiz waiters about edible ungulates. It’s pathetic. My rationale is that staff should be knowledgeable about menus (and so they should), but I also admit to something horribly geography-teacher, Friday-quiz about this. What’s worse, I never order it.

Anyway, I’m in full geography-teacher mode when I notice that there are frogs’ legs on the menu. I catch the waiter’s eye. Nervously, he approaches the table, zigzagging.

The frogs’ legs ... “Yes?” Where do they come from? “Frogs.” Nice try. It says here they’re from the Ardennes.

“I, too, am from Belgium,” offered the waiter. I badly wanted to ask if he had frogs’ legs, but I didn’t — and I hope St Peter has made a note of it. “I’ll go and ask.” He cut for the kitchen, returning, I noticed, a little dishevelled, as if someone had held him up against the wall by his lapels. “They are definitely from the Ardennes, chef says.” Fine. Well, we’ll have some, then.

This wasn’t like the deer question. The frog question has a point. The European breed of edible frog is rare, and although Belgium does have a little frog harvest and exports a few, Europe as a whole imports 6,300 tonnes of frogs’ legs a year. France consumes 3,500 tonnes of them. Seeing as each pair of legs can’t weigh more than a couple of ounces, that’s un grand mess de frogs. There used to be bullfrogs from Bangladesh and India. Now, though, almost all of them come from Indonesia. Bangladesh, one of the poorest countries in the world, banned the export, along with India, because the rise in crop-eating creepy-crawlies made it uneconomic.

And here’s the good bit: Indonesia now has to import 25% more pesticides to make up for the absence of frogs. It’s estimated that a smallholder in a sarong has to use $5 of pesticides to harvest $2 of frogs, and that the country spends $30m to make $10m. Still, it’s not all bad news. Guess who sells them the pesticides? Now European chemical workers can afford to eat frogs’ legs and the Indonesians get new sorts of cancer — and the chance to take part in free trade.

Oh, here come Kermit pieds, so no need to fill our pretty little heads with all that. Mmm, they’re delicious. So clever of Marcus to find the only Belgian frogs with gout.

Let’s avert our gaze and think of higher things — like the red-velvet wallpaper. Pétrus has moved to the Berkeley hotel, where it has been done up by David Collins, who appears to have been inspired by the inside of his jewel box. And who wouldn’t be? Stuck into the red plush are lights that could have been dodgy 1950s cuff links. I yearned for a plastic ballerina to circle in the middle of the room on a mirror to the sound of the Blue Danube. It all made me feel a bit like a rejected engagement ring, but the tables are a good size and well spaced — though oddly, some chairs have arms and others don’t.

The old Pétrus was one of the few restaurants I’ve given five stars to, and I see no reason to reconsider. I still think Wareing is probably the best chef in London who’s still fiddling with froggy members. The menu is a joy of restrained aesthetic opulence. Wareing’s great talent is in knowing precisely when and where to stop. There’s never a flavour out of place or a de trop garnish. You can eat off the carte for £55, or you can do what I did and choose from the set lunch menu: three courses with twiddly bits for £26. And that is the best deal in London. Go now. Go often. Don’t tell your friends. Rip this page out of the magazine before your wife sees it.

I’m not going to single out dishes — just one amuse-bouche. Normally, I hate these little bits of impertinent, inter-course palate-frotting. But a glass of tomato gazpacho flavoured with pineapple and vanilla was shout-out-loud amazing. I did shout out loud, which is what attracted the waiter, which is why I had to do the deer thing. If they put vodka in this soup, they’d never sell another bloody mary.

Anyway, Pétrus. A benchmark. A frog in a velvet box.

Lunch, Mon-Fri, noon-2.30pm; dinner, Mon-Sat, 6-11pm

Times Recommends

• Britain's Top 20 seaside fish and chip shops
• Ice cream makers: the scoop of the century
• British berries make super sorbets