A confident, glamorous London townhouse designed by Bryan O'Sullivan

You can frame a story in any number of ways. Take the interior of this early 19th-century terraced house in one of London’s smartest postcodes, designed by Bryan O’Sullivan. It could be described in terms of its spatial and architectural merit: how original features were researched and sensitively reinstated, while new floors and half-floors were created with confidence and ingenuity.

Built originally as four storeys, including a basement, the house has grown in size over the years and now has a mansard roof, an extension and, more recently, an additional basement level. There have been several bold choices, such as the central skylit void, which houses a winding staircase and marks the meeting point of the old house and the modern addition. Before working for the likes of David Collins, Martin Brudnizki and Luis Laplace, Irish designer Bryan, who founded his eponymous interiors studio in 2013, studied architecture in London, where he is now based.

Another tack might be to see the house as the apotheosis of an evolving partnership between designer and client, which has developed over multiple projects in Paris, New York and Dublin. And very design-minded the clients are. ‘They always come to the table with ideas,’ explains Bryan. ‘So, in many ways, it’s an opportunity for me to consider things I might not have come up with on my own.’ Though this is not their only home, the collaborative process has allowed it to be decorated and filled in a way that gives a feeling of permanency and personality, rather than simply of convenience and comfort.

Instead, let us look at this house as a celebration of materials and texture and how they can do more than just intrigue the eye of the beholder. When chosen judiciously – yet with flair – these can dictate the character of a room, influence the mood of its inhabitants and change the way sound travels within the space. It is one of the defining qualities of the house and is at its most tangible in the basement immediately below the ground floor.

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The kitchen is at the back of this big, bright area, and it is a glorious melange of materials concocted together with the bespoke furniture maker Rupert Bevan. Woven and mesh brass have been used on drawer and cupboard fronts, while the same metal creates a mottled effect on the kitchen island. The pocket doors of a built-in larder are clad in white plaster and work beautifully with the honed Serpeggiante Avorio marble floors and Calacatta marble worksurfaces. Elsewhere there is oak, which has been stained grey on the wall cupboards and sand-blasted on the island. Yet the scheme retains a simplicity – it is modern with artisan flourishes. Through Crittall doors, which open onto a sunken terrace, can be seen a variegated living wall covered with plants.

Moving towards the front of the house, past the new central staircase and up a few steps, we are back within the original footprint of the building. The ceiling is much lower here due to planning constraints, and it is not a space blessed with much natural light. This inspired the distinct change in decorative mood. ‘We decided not to fight the character of the space,’ says Bryan. ‘It is a cosy, cocooning area, so we have played to its strengths.’ A dining area has patinated grey-green plaster walls and there is a richness to the elegant pieces that fill it, from the original 18th-century Siena-marble-faced chimneypiece to the Greek Revival klismos chairs and silk ikat rug on herringbone-laid wooden floors. A blackened steel architrave along the top of this and the adjacent room adds a cool, contemporary touch.