Selfridges is skilled at making things that are not hideous (women) look hideous (women dressed as Bungle from Rainbow or a tree, after shopping at Selfridges). So I was not surprised to discover that it has summoned a ‘pop-up’ restaurant to its roof. It is called Vintage Salt and it is based on a Cornish fishing village. Not a real one, such as Newlyn, but a fake one, such as Padstow, which is based on Selfridges anyway. Selfridges shoppers do not want reality but a half-remembered contortion of something they read in Vogue while having their hair dyed banana yellow in St John’s Wood High Street in the company of a chihuahua smarter than they are.

The portal is an express lift in Fragrance. This is the point, I suppose, at which Vintage Salt and Newlyn part company, if ever they met — when I pass a group of women in ink-black burkas and Dior handbags spraying perfume over themselves, because then they will feel different. This is, essentially, the lie of advertising, which Selfridges screams better than anyone; if you pay to smell like Toilet Duck you will be worthy of love. That they have exactly the same Dior handbag is, I suppose, a nod to the philosophy of the burka. I do not hate all department stores — I like Debenhams — but Selfridges is quite close to a cult of idiocy. Its mantra used to be I Shop Therefore I Am. As manifestos go, that is sub-Boko Haram.

The lift contains a woman dressed in a striped Breton top. Brittany is not in Cornwall. Upstairs, a long and tatty corridor, lined with small boulders and piles of rope. It is slightly Hornblower-esque. At the end, an anxious reception desk staffed by women in cream dresses. They repel a couple without a reservation, without charm.

I am taken to a seat between a sheet of plastic, an open kitchen and a speaker. I ask to move. The girl in cream refuses, with the sort of blank-eyed contempt a 40-year-old woman will only ever see in the face of a 20-year-old woman inside a high fashion department store with a fake fishing village. I loathe her, because if I were younger, and better dressed — I am dressed as tarmac, actually — she would have acquiesced. I apply to her superior. I am moved.

The Selfridges rooftop is fascinating, for a rectangle; I sit beside the huge flags shadowing Oxford Street — a late-capitalist United Nations committed to the security of Fragrance? I watch the cranes dissecting Mayfair. The August clouds are purple, summoning the devil. Where is the sea? It must be in Southend. There are beach huts and nautical-themed engravings and bits of quasi-fishing tat, designed I suspect by someone who has never seen a live mackerel. It is a collection of whimsies floating with the deftness of boulders flung to earth. It is too much even for Selfridges, which is not, by its own design, a real place. It should be a jazz bar.

The restaurants in Cornish fishing villages nowadays are filled with stripped-out Scandinavian-style interiors or pale blue cashmere blanketry. They are, of course, impersonating London; and now Selfridges impersonates them as they impersonate her. That is a massacre of identities entirely typical of fashion people.

The food, just, holds up. Shrimps look like the customers, who are all 25 — thin, orange, big hair — and are very good. Chilled tomato soup with mozzarella is acidly, truly chilling; T-bone is too cold from the fridge. I wanted it blue but hot blue. It feels like a tongue.

I order a chocolate burger. It is a scone, with chocolate slab and something gross impersonating tomato and then cheese; the chips are elongated doughnut. I have not eaten a dish so foul in all my days of restaurant criticism. This, then, is where whimsy comes to die.