A 19th century mansion beautifully modernised by Rabih Hage

When the owners of this grand late-nineteenth-century house, situated in a west London square, moved in some 10 years or so ago, they did little more than give it a decorative overhaul. A decade on and much in their lives had changed. They now have a young child, and the five children from their first marriages have grown up and need more autonomous spaces during their frequent visits home.

Aesthetically, too, they had moved on. It was not just that the house had grown slightly shabby in the intervening years, but the owners wanted a look that was cleaner, less ornate and less decorative. They had heard of the work of architect and interior designer Rabih Hage, and they liked the fact that he combined the two disciplines. As an architect, he could rethink the way the house worked and reconfigure its spaces. As an interior designer, he could give the interiors a classic, timeless feel. The owners were also confident that his contacts with artisans and craftsmen could provide the essential touches of magic.

For Rabih, it was a wonderful project. The house was one of the few in the square that had not been divided up into flats. It has large, airy rooms, many complete with original cornicing and chimneypieces, which were both challenging and inspiring due to their scale. But it needed a complete rethink to make it work.

They were lucky that, although the house already had a lower ground floor, they were able to get permission to build another floor below that. This meant that in the new basement, Rabih could provide for the family's leisure activities, with a temperature- controlled wine cellar, a gym, a spa area, a bar and a cinema with seating for eight.

At the front of the house, on the lower ground floor, which has private direct access from the street, Rabih created a self-contained flat with its own small kitchen for the wife's grown-up son. This way he can come and go as he pleases without disturbing the rest of the house. Behind this, there is a room for flower arranging and, at the back, leading out onto the garden, an informal sitting room ideal for watching television, reading and playing games.

Meanwhile, Rabih had decided the ground floor needed to be completely rethought. The clients loved the grandeur of the entrance hall and wanted marble floors, so Rabih tracked some down in a gentle neutral tone, teamed it with a pale linen paper and, as an alternative to traditional crystal chandeliers, chose two large and lovely papier mâché ones by Studio Job for Moooi. 'Though imposing in size, they add a light - and slightly subversive - touch, which does nothing to affect the grandeur, but stops it being too conventionally opulent,' says Rabih.

He also decided to reverse the rooms on the ground floor, moving the kitchen from the back to the front and the dining room to the back. 'I thought it would be much nicer for the kitchen to face south over the square, so I put a small table by the front window where they can have family breakfasts,' he explains. Since the family is quite large and they do a lot of entertaining, there is a small, professionally equipped area at the back of the kitchen where food can be prepared away from the family. An Ingo Maurer gold-leaf ceiling light hangs over the main area for food preparation, behind which is ample storage for all the kitchen paraphernalia.

The dining room has several functions. It can be a grand setting for entertaining - a quirky light fitting made from metal threads by Terzani hangs over the Victorian table, bought from The Furniture Cave on the King's Road 15 years ago, and there's a made-to-measure Piet Hein Eek sideboard. By the window, there is a smaller table for intimate dinners or tea for two, as well as seating with views out over the garden.