It has always fostered new talent and visionary ideas – particularly in the field of design. It has wowed shoppers with a programme of theatrical fantasies staged behind the finest stretch of shop-window glazing in London. And, by rights, it should be remembered as one of the great innovators of 20th-century retailing.Simpson Piccadilly was founded by Alec Simpson, son of Simeon, an enterprising Petticoat Lane tailor who pioneered factory- made ready-to-wear. When it opened in 1936 it claimed to be the largest menswear store in London – possibly the world.According to one newspaper, the enterprise was “a bid to right the balance of sex equality”, by offering an all-blokes shopping experience in a setting “that is congenial and heartily male”. A womens-wear department was installed less than a year later, but the store started life as a temple of collar- attached shirts, DAKS slacks and macs, cotton Y-fronts (an American import) and two-piece suits with zippered, self-supporting trousers and single-breasted jackets – all cutting-edge stuff at the time.

We owe Alec Simpson thanks for liberating men from starch, studs and baggy pants.Alec Simpson was a true modernist, and his taste for the new was reflected in every detail of the store – from the chrome light-fittings (when chromium- plate was still a bright young thing) and the strips of neon which decorated the exterior, to the vacuum-driven “Lamson Paragon” system which whooshed cylinders of cash between sales points and sixth-floor cashiers.The building was designed by Joseph Emberton and, under Simpson’s guidance, was variously influenced by the art deco movement, the Bauhaus School and the work of the Chicago architect Louis “form- follows-function” Sullivan. It would have been a first for the high street.It would have been a fitting end, too, because being first is part of the Simpson culture. But is it a fitting epitaph to this retailing institution? Not exactly.When Sarah Southgate learned of the store’s imminent closure (on 30 January; it is to be the flagship of Waterstone’s book empire), she was planning her own visual swan-song, based on illusion and combining a variety of technical tricks (lights, projected images, a few trade secrets) to enable passing window-shoppers to interact with the scheme through movement and touch. A prelude to the store’s January demise, the theme is “Good Buy, Good Buy”. It manages to say “farewell, Happy Christmas and roll up for the final clearance sale” in one lavish party of props borrowed from the festive windows of Simpson’s last three years. Someone else has locked the display manager, Sarah Southgate, into one of the lobby windows with a papier-mache trapeze artist and a clown with Christmas-tree hair. “Come on guys, let me out,” she cries.It really ought to be fun.

But just below the surface of banter and tinsel lies an unseasonal air of despondency This is Simpson Piccadilly’s last ever window display. A large pink rabbit with a top hat and a Salvador Dali moustache has emerged from a cocoon of bubble- wrap. “Careful,” says the electrician, “that window’s listed.”Behind the scenes, someone is packing a crowd of po-faced albino mannequins into the service lift. Then I crack my head on a curve of Simpson’s famously non-reflective glass.