Sue Crewe's London house | House & Garden

I have come down in the world. I used to live on the top floors of my London house, with a garden on the roof, and now my flat is on the ground floor, with a tiny garden leading off the sitting room. To be honest, I was getting a little weary of lugging suitcases and shopping up the stairs, and it was a chore taking compost up to the roof terrace. I am getting older and one day I hope to be really old and old people last longer if they do not fall down stairs. So I decided to sell the top floors and use the proceeds to pull apart the ground floor and reassemble it. My daughter had the foresight to marry a brilliant architect and I have the good fortune to have a cousin who is a brilliant decorator and also a dear friend, so choosing whom to enlist on the project was not a problem.

It might have been risky to work with relations and friends, but we were clear about costs and responsibilities from the start and set up a buffer zone between client, architect and decorator. My son-in-law James Gorst drew up the plan and then handed the running of the year-long build to one of the senior architects in his practice, Laura O’Brien. She was so assiduous, imaginative and fun that I wish I could embark on another conversion just for the sheer joy of working with her. Likewise, my cousin Jane Ormsby Gore of J R Design, who created the overall scheme for the decoration of the rooms, while her principal designer, Charlotte Allison, oversaw the implementation and looked after the 101 details and day-to-day decisions.

It was probably helpful that I knew what I wanted, which was a main bedroom with an en-suite wet room, a spare bedroom and bathroom, a room that would be used as both a dining room and study, a kitchen and a sitting room with a working fireplace. This was a tall order, because the available space was tight. James magically achieved it by extending over the side return, removing a wall that held up the entire house and inserting roof lights in the bedroom and kitchen ceilings. The builders, Cubitt Theobald, had a hellish time working in a confined space during a wet winter while tons of steel was manoeuvred into place, but they remained cheerful and considerate throughout.

There were unforeseen setbacks, of course, and the whole thing took longer and cost more than I had expected, but that was probably because I was reluctant to compromise. What did rather shake me was the amount of money I had to produce before anything happened. Things like party-wall agreements, structural engineer reports, asbestos removal and fees for this and that all mounted up, and I had nothing to show for it.

However, when the site stopped looking like a wet hole in the ground and walls started to go up instead of down, my spirits soared. The west-facing sitting room is light with pale walls. The back of this room is the dining room/study, which has no natural light. Instead of fighting this, we made it a dark red cocoon hung with seventeenth- and eighteenth-century portraits. Cubitt Theobald made red lacquer cupboards and shelves that contain my whole life. It is no accident that everything fits in. Between them, Laura and Charlotte measured and counted my possessions before they went into storage so that when they emerged again, everything had a place. Similarly, the tiny kitchen, which was designed and built by Neptune – I think it may be the smallest kitchen it has ever made – functions perfectly and two sets of pocket doors enable it to be closed off or act as a passage.

There are so many things that I love about my flat: the smooth tadelakt walls of the bathrooms; the hand-painted tree on the wall of my bedroom, upon which perch Cumbrian birds; the beautiful tiles by Bert & May on the kitchen floor; the Thirties fabric of the sitting room curtains; the wild stripes on the walls of the passage. All this and more ordained by J R Design and applied to the light-filled, fluid space created by my clever son-in-law. Lucky, lucky me.

JR Design: 020-7221 9048; jrdesign.org
James Gorst Architects: 020-7336 7140; jamesgorstarchitects.co.uk
Cubitt Theobald: 01787-371002; cubitt.co.uk