There are two types of homeowner: those who are averse to any kind of makeover project and those whose heart beats faster at the sight of a house in an extreme state of dilapidation. Jane Churchill, the interior designer, has already rehabilitated eight down-on-their luck properties. But she is now preparing to take on another. It is true that her revamped homes have served as shop windows for her business. However, equally commercially minded people would have weakened some time ago.

The only obstacle in her path towards her ninth change of address is the rarity of fixer-upper houses in Central London. In late 2004, the market in the capital was in the doldrums, which allowed Mrs Churchill to find a run-down boarding house in Belgravia, minutes away from ultra-smart Eaton Square. The luxe refurbishment boom of 2006-07, financed by City and international money, has made it much less likely that you could ever again find a similar dump in an elegant neighbourhood.

However, Mrs Churchill remains confident that, somewhere in Chelsea, Kensington and Knightsbridge, an underachiever period property awaits her attention and so she is selling the four-storey Belgravia house, which was built in the 1840s, for £4.5 million. Her next project will be on a smaller scale than her earlier efforts; she is “paring down” - other people might call it “downsizing” - as the last of her three sons (all of them employed in real estate) is bound for a place of his own.

Mrs Churchill has been separated for some years from her husband, Lord Charles Spencer-Churchill, the younger brother of the Duke of Marlborough. Whether or not as a result of this marriage, her designs are decidedly grand, but not grandiose. Whether she is creating something for herself, or for her clients (the great, the good and the rich) her aim is to produce “something you want to come home to”, with plenty of storage.

The Belgravia house, sizeable but still cosy, exemplifies this principle. Before Mrs Churchill and her team of builders, cabinet makers, curtain specialists, decorators and so forth set to work, the drawing room on the first floor was divided into four wretched bedsits. The kitchen was in that state of squalor which inspires rather than repels those with the restoration urge in their DNA.

Today, the drawing room is once more a pristine single space. The walls are painted in a chalky, grey-ish shade and an abstract painting hangs over the colossal sofa; the furniture and furnishings are a mixture of antique and modern with scarcely a trace of the extravagant florals traditionally associated with the Jane Churchill aesthetic. Mrs Churchill opened her interior design shop in Pimlico Road in 1983; for this reason she is supposed to be inextricably attached to the chintz and swagging of the era.

“Actually,” she says, “I prefer an eclectic feel, bit of old, bit of new. A total minimalist look is OK when you are throwing a party and the room is crowded, but it's too much when you are on your own in that room.” Plenty of cupboards are another essential of the Churchill aesthetic, but they are never fitted, as that would be a bit downmarket.

The boarding house's tenants would not recognise the drawing room, or any other bit of their former lodgings. The lower ground floor has been turned into a light-filled, self-contained two-bedroom flat. The ground floor has been extended to provide a dining room which mostly serves as a library (as Mrs Churchill puts it: “Who wants a dining room that's only a dining room nowadays, unless they have hot and cold running staff?”); a kitchen and, across a small Italianate courtyard, a garden room used as a bedroom. The current standard Belgravia kitchen, as favoured by hedge fund managers, is a stainless-steel creation, typically fitted out by Pedini, the Italian manufacturer. Mrs Churchill opted for something less proto-industrial; the wooden-doored units are painted in a pale cream shade; the walls in a light amber hue - which even a fan of sleek modernity would find quite peachy.

The standard Belgravia hedge fund manager bedroom exactly resembles a five-star hotel suite; Mrs Churchill says that even her clients sometimes request this hospitality-industry look. Her own preferred style is the bedroom as retreat, rather than staging place. The spacious but snug master suite bedroom on the second floor and the equally comfy bedroom on the top floor represent the fulfilment of this plan. Until the next time, that is.

Strutt & Parker, 020-7235 9959, struttandparker.com

Top tips

Jane Churchill advises: Whatever your budget, your aim and object should always be to create something that you want to come home to. This may sound obvious advice, but it is often forgotten.

Spend your money wisely: a good sofa, a good bed and a good bathroom should be your priorities: a down-filled sofa may be more expensive but it pays off. Think hard before you do any work or make any purchase: it is easier to add to a house than to take away.

Keep a file of designs and things you like. My bundle of pages torn out of magazines is one inspiration, but I based stencils on a pattern I have seen in the Ashmolean Museum in Oxford, for example.

Your inspiration can come from anywhere: the tassles on the curtains in my drawing rooms are based on a sweater that one of my colleagues was wearing.

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