Langan’s Brasserie announces its presence with a long, pink neon line of Langanses, tootling prettily along its façade, which is opposite Marks & Spencer on Green Park. (The apostrophes, by the way, are mine; signage can be illiterate.) So this is a restaurant with Alzheimer’s, a restaurant that has forgotten its own name.

Could it be hungover? Langan’s was opened in 1976 by Michael Caine, Richard Shepherd and Peter Langan; two thirds of the triumvirate were newsworthy. Langan was the sort of alcoholic who is mistaken for a raconteur: he told Orson Welles he was fat. (He was fat. Do we care about the feelings of Orson’s fat ghost?) His alcoholism became a destination in its own right, because people are cruel. Langan’s was, for 15 minutes in about 1981, the centre of the earth.

And now? Other fashionable brasseries have opened — principally the wonderful trio of Zédel, the Delaunay, and the Wolseley, which is closed for renovations but still retains its cadaverous doorman, who is grimly admitting tins of paint; Novikov, a screaming exhibitionist which is also an Italian/Asian restaurant, is bigger. So what of Langan’s, still hanging on to the fringes of Mayfair?

It is soft at the edges — a rectangular cavern, warm but faintly yellowing. It feels dramatic, a destination restaurant in some circles, still got it; before the food arrives. There is a chaotic cloakroom and elderly waiters in black, always reassuring — but look closer: carpets are fraying; corners are dusty; the bathrooms are over-bright, like an explosion; the art, once so talked about, is not the best. Langan’s art collection, including a terrifying Hockney of Langan himself, staring at the painter with agonised eyes, groping for his glass, was sold in 2012. ‘Peter Langan: A Life with Art captures the inextricable fusion of good food, good wine and good fun with good art that is synonymous with the legendary hot spot,’ said Christie’s, moronically, possibly oblivious to the fact that before he died at 47, Langan tried to burn his house down.

The clients are as if dining in 1982: big bottle blondes with armoured chests and golden, sagging skin. They are self-consciously sexy, even if I think of them as glittery velociraptors (they look like they eat their husbands); bald, fat men in black suits, with tax lawyers and tiny yachts. It is a rampant, shagging, cruise-ship crowd who come here often because they always have; there must be deaths.

The menu is a stagger through the unthreatening, the familiar and the beloved; soft food, posh nosh and a bit of forgotten Italy, where once they went. So here we have steaks, burgers, lobsters, fish pie: a big menu, designed by David Hockney I was told, hard to pull off, but trundling along with the engine of some ancient, James Callaghan-era charisma.

J. orders field mushrooms with bacon and Lancashire cheese; I have a Caesar salad. It takes ages, so we attack the white bread rolls; when did we last see white bread rolls in a living restaurant? These are semi-mythical; they are constantly replaced, Prometheus’s liver in flour, due, I think, to the (£2) cover charge, another anachronism staggering out of the past. Now it comes: mushrooms in a soup of cheese; fondue mushrooms with evil intent. My salad is simply a bread salad; the croutons are large as ships, capable of making Peter Langan stand up.

Now comes sausage and mash, and fish pie. The sausages are greasy, on a bed of over-buttered, possibly microwaved mash. The fish pie is ferociously orange; it collapses under the fury of dill. I did not know that dill could be aggressive. Langan’s is, essentially, Oslo Court for gentiles; it collapses under the weight of its own memories.