How must if feel to walk into your office one morning, sit down at your drawing board – and come up with a design classic? I wonder if you get a sense that this is something special, perhaps your best ever work – or whether that comes later, after the acclaim.

I am simplifying, of course: the creation of a significant item is not the work of one day, even though the initial concept can perhaps come remarkably quickly. There is a great deal of research and development, material testing and more that goes into the realisation of a top-quality product.

It is twenty years since Antonio Citterio, the Italian architect-designer did just that with what has since become the iconic piece that made his name around the world: the Charles sofa for renowned furnishing company B&B Italia. It has done the same trick for the company, becoming by far their best-selling piece.

Inspired by the designs of the Sixties and named after Charles Eames, this has become an icon of contemporary design, the symbol of modernist-minimalism par excellence. Put one of these in a room and it will immediately set the agenda. This is a piece that has been copied a thousand times: If you have ever seen a sofa that is low, deep with spindly metal legs, then the chances are it is a derivative of the original Charles.

Having admired from afar, I first encountered one ‘in the flesh’ at Geoffrey Drayton’s showroom in Hampstead Road, London. My wife and I were at the stage of establishing our first home together, and seating was naturally high on the agenda.

There is something about this piece that is so close to modern perfection that it utterly deserves the recognition it has received. The fifteen-degree angle at which the sides slope is exactly right, as are the proportions of the inverted-L aluminium legs and the slimness of the base. The combination of rich fabric and polished metal, of tightly-tailored base and loose, movable cushions is another sensory feast. The raised base frees-up floor creating a sense of spaciousness, and the reflectivity of the legs creates a floating effect the seat itself. To my eye, this is a piece of design perfection that even Citterio’s other designs don’t get near.

Testing it after walking around half of London was probably not the best move; some British and American commentators have found it too firm for their liking – but firm support is actually our preference, over the traditionally squishy British alternatives. It’s interesting to realise that even notions such as comfort are to some extent culturally-defined.

Charles is a modular concept: there are numerous shapes; it has also spawned an extra-large range (as it if were not big enough already…), a bed, low tables and an outdoor version. It is not something, however, that is easily accommodated in the average tiny British sitting room – it needs space to breathe.

Unsurprisingly, such pieces do not come cheap; this is best considered a once-in-a-lifetime investment. At least it has more mileage left in it than the average used car… Beneath the slim profile is a welded steel frame, and a high-density moulded foam carcase: they should last forever. The same cannot be said, however about the fabrics, which are more beautiful than durable. At least the covers are removable…

Charles is not a sensible financial investment, but it is certainly an aesthetic one: it creates a stylistic agenda for the rest of the home; in that sense, it is worth cutting corners elsewhere for. It has visual qualities that succeed in numerous different environments and its character and proportions are so perfect that it will lift whatever space it is placed in.

This is one piece of design of which I simply never grow tired.