Highgrove is the country house of the Prince of Wales. I write about Highgrove because, although it is not a restaurant, even of the wackiest kind — which can only make me fantasise that Ludwig of Bavaria opened a gay sauna in Neuschwanstein castle — the prince does admit strangers when he is not there and only when he is not there: on Burns Night for instance, or Mothering Sunday, and now, on St David’s Day: a black tie dinner for £95 per face including service.

The dinner is in a custom-built barn in the Hobbit style. It is made for his receptions, so I suppose it is less a barn than a giant all-weather gazebo which they call the Orchard Restaurant. (This is not as terrible a fate as you might imagine for the royal out-buildings: King Henry VIII’s tiltyard at Hampton Court is now a caff). Of course they won’t let us in the actual house, but the Orchard Restaurant is a barn/all-weather gazebo/restaurant with drama; there are lamps outside.  Inside, in an anteroom, a gathering of perhaps 80 people, of exactly the sort you would imagine dining in Prince Charles’s all-weather gazebo when he is not there, humming with social anxiety and expectation, having read the Q&A on his website: can I bring more than 26 guests? Can I bring bino-culars? Can I perform an internal examination? I instantly think: this is a party designed by Pippa Middleton of Celebrate! (top tip: when dining near Highgrove, do not wear a Team Diana cummerbund). Except everyone seems terrified, as if the prince might appear as a surprise guest. There is champagne, excellent canapés, a cloakroom, a harpist, a charming greeter and his watercolours all over the walls. His watercolours, which are largely of his mother’s houses, or glens, are very good. They express a delicate sort of rage.

We are ushered in to the — well, is it a salon? A converted pigpen? Bah, he’s got taste, this one, or has hired someone who has. There is one rectangular table, covered in grey crushed velvet, huge bowls of daffodils, and clear glass candlesticks, the cleanest I have ever seen; so we dine together in the medieval style or maybe it’s simply Downton Abbey. (I don’t even want to think what percentage of the customers are fans of Downton Abbey. Maybe 103 per cent?) My next-door neighbour, who is grave and charming, says his wife used to smuggle yeast into Saudi Arabia in her boots. I think this makes her an international baking smuggler; although he says it was for alcohol, not loaves. There is a real fire, and immense portraits of the royal family on the walls, gazing remotely; the Duchess of Cornwall is smaller than the rest, but more centrally — and very pointedly — hung. The effect is beautiful, but of course I pull up the grey crushed velvet and there are metal trestle tables underneath: that is monarchy. This makes me think of the late Queen Mother, who was sometimes called the Steel Marshmallow; and this is her memorial trestle table.

The food is excellent, almost depressingly so, and comes in a series of tiny courses, in the manner of a man who might be a course maniac, but still wants, beyond all things, to be thin: leek and potato bread (one piece only), cauliflower and smoked butter velouté; Glamorgan sausage with Duchy Farm egg and leek salad; roast rump of lamb; Llaeth Y Llan yoghurt and Usk Valley honey panna cotta. It is all tasteful and fragile, as he is; but the coffee is terrible.

We do something I have never experienced in a restaurant: we are invited to rise and toast the owner. I must remember to do this to Richard Caring next time I am in Scott’s; or to the Colonel when in KFC.