As far as seals of approval for a restaurant go, they vary widely person to person. Some diners follow Michelin stars like they’re signs from God, others take recommendations from their favourite magazines or foodies like gospel. But for some, restaurants blessed with patronage from the late Queen are the pinnacle of culinary necessity. Bellamy’s, hidden down a side road off Berkeley Square, is one such place.

You won’t hear much about it from patron Gavin Rankin, though. The height of discretion – “We don’t comment on any of those sort of aspects”, he tells me – it’s easy to see why the restaurant may have been chosen by the royals, not simply for the impeccable food and warm, comfortable interiors, but also for the fact that once inside, what happens when she dines will remain a secret held by the staff and the four walls of the restaurant.

Opened 18 years ago, Bellamy’s is, in many ways, an expression of Rankin himself. It was designed to emulate the brasseries of Paris – large, bustling places that feel lively yet comfortable, where you’re always welcomed like a friend and the food is faultless and reliable. “I've loved brasseries all my life,” Rankin tells me. “There was something sort of free and easy about them, I suppose. I asked a French friend to define a brasserie once, and he said it was very simple: you walk in and there’s a feel of activity, things happening, glasses clinking and cutlery being sorted. Then there’s a sort of feel of ‘can do’. You know a table turns up and it’s ‘Oh, we’re six, not four,’ and chairs have to be brought head height across a crowded room. And then there’s the smell of food, not of cooking, but of food. And you think ‘Oh, there could be an oyster here, or a lobster or something. And I think that’s it. The idea that there could be a chap in jeans over there, or a chap in a dinner jacket over there, you know it’s sort of a great coming together. So that’s always appealed to me.”

I've loved brasseries all my life. There was something sort of free and easy about them

It’s a feeling that he has successfully captured in Bellamy’s, albeit with a slightly more English sheen – that precise air of Parisian chaos not being so translatable into a London setting. For Rankin, though, the integral part that has remained is this feeling of everyone being welcome. It would be easy for a storied brasserie in this area to feel inaccessible for a younger customer or someone not dressed to the nines in a dinner jacket and tie. In fact, many places in the area are just that: exclusive and stuffy. Bellamy’s, meanwhile, aims to be the direct antithesis. There is no dress code, staff are friendly no matter how much you might be spending and the wine list is almost criminally well-priced – both the red and white wines kick off at an accessible £29 for good-quality bottles.

“All the best parties have young and old together anyway,” Rankin laughs. “But, I mean, everyone remembers the snooty head waiter that tormented them the first time they took someone out for dinner. We like to take a different approach, because today’s very young person is tomorrow’s heavy customer. They might say we treat them special, you know, saying ‘your usual table’, that sort of thing, just picking them up a bit. Obviously they don’t have as much money, and they’re choosing to spend it with you, so if we can nudge them into the cheaper part of the menu we will. We’re not here to just fleece them.” It’s something I saw in action during my meal, the young and the old sitting side by side, no haughty glances or twenty-somethings sweating over the menu and doing mental calculations. Instead, waiters and waitresses deftly tone-shifting between customers, ensuring everyone was thoroughly enjoying themselves.

While Rankin has been at Bellamy’s since the beginning, so has chef Stéphane Pacoud, who came over from the Birley empire with him to launch the restaurant. Reading the menu, you’ll notice particular dishes are written in a raspberry-coloured font, pulling them out to you. These are the dishes that, as Rankin says, “are the basic staples on the menu, that we’d be in a lot of trouble if we took them off.” They are items like the iced lobster soufflé, a ramekin of food so naughty and delicious it feels like a true indulgence and yet manages not to be too much, and the Dover sole with oil, lemon and pommes vapeur , which, as Rankin says, is the perfect representation of Pacoud’s ethos that “you are naked under the spotlight, so there are no elaborate sauces to hide behind. It’s all to do with the ingredients and how they’re assembled.”

He tells me the story of the smoked eel mousse – one of the dishes written in that buoying raspberry font – and its origins. It’s a tale that is a true testament to the sheer talent of chef Pacoud. “The smoked eel mousse is one of the longest running dishes on the menu,” Rankin tells me. “Quite frankly, we stole it from a restaurant in Brussels that was dripping in Michelin stars. We went there for lunch one day and I was eating the smoked eel mousse. I should say, chef (Pacoud) has perfect culinary pitch, I mean – he can disassemble something by tasting it, work out how it was done, and then reassemble it, often for the better. Anyway, I was eating it and I said ‘This is great.’ And he leaned over, and stuck a finger in my mousse and tasted it. And then it was on the menu three days later and has been there ever since.”

While much has remained the same, the menu has changed in bits and bobs over time. Rankin holds the intelligent opinion that “in order to stay the same, you have to change.” And while this change may come in subtle increments – a new dish here, an upgraded wine glass there – it helps guide the restaurant through the years, staying true to its intentions while successfully sailing into the modern day. As Rankin says, “the primary job of a menu is to seduce,” and the Bellamy’s menu is perhaps the greatest seductress of them all.