The trek, however, would be more than worth it were it twice as tricky. At its end lies a jewel of a barn guarded by a perfect oak. Virtually all old Sussex barns used to be built on an east-west axis to allow the wind to move through their main doors to separate the wheat from the chaff. Today, it’s the manner in which they’ve been converted which differentiates between wheat and chaff. This conversion is serious wheat.

The attention to detail begins at the front door where visitors announce their arrival not by the push of a button but by the ringing of an old, hanging maritime brass bell. An old school hand-bell is offered as backup. The summons is answered by Molly who has taken almost five years to take the barn from working barn sheltering livestock to exceptional family home.

“We used to live in an idyllic location on the Marsh but the access was terrible,” she grins. Before the Marsh, the family home was a beautiful 1928 house and farm in Sussex built by her husband’s grandmother, but ultimately the upkeep proved ruinous.

“It was my idea to sell and so I’ve always felt I was responsible for finding – or creating – a new family home,” she says. And that is exactly what the barn now is – a home, too, for the family pieces now in their care.

Creating a space which fulfils both roles so well has been no mean feat. This is no huge, rambling hall of a barn but a relatively small, three-bay building where either primary objective could have so easily been compromised. Even on short acquaintance, however, one quickly appreciates that compromise, as verb or noun, is not in the vocabulary.

Faced with a shell, Molly set about planning exactly how each piece of furniture, each painting or sculpture would not only fit in the new space available but be done justice and presented in the manner they deserve. Clearly, it would be a challenge.

“I woke every morning for months thinking in inches,” she says. “In effect, I designed the house around key pieces but always remembering that it wasn’t to be a museum but a real home.” She had not only to juggle space, furniture and function, she also had to satisfy planning and building regulations.

“In the end, I knew exactly where everything was going to go – and then it was just a matter of getting it done.” Ultimately, getting it done exactly the way she needed it done took more than four years, much of it living in a caravan on site.

The result is a triumph – a living, breathing family home, furnished largely with beautiful possessions much loved through the centuries. Extraordinarily, despite the fact that this is not a big barn and now houses countless lovely pieces, never anywhere does it feel the slightest cluttered – in fact, exactly the reverse. Everywhere there seems space – and light.

Light in any barn conversion, even the largest, can be a problem. Planning regulations dictate that windows can only be placed where openings in the walls already exist. Since there was little call for particularly brilliant lighting in what were, essentially, big agricultural sheds, this can be a major problem. Molly has solved this problem first by making the most of the original openings – both the south and great north doors are now glass ­– and then cleverly creating interior windows that channel borrowed light from the upper floors down to both kitchen and drawing room.

Molly is now a true reclamation junkie, and entering the front door, one’s greeted by one of her greatest finds – a magnificent oak staircase which, while far too grand ever to have started life in so humble a building as a barn, gives the impression of having stood solidly here since Genesis. However, although grand, it has been naturally distressed by wind and weather until it now perfectly complements the old timbers in the roof and walls that surround it.

“I bought the whole staircase at a reclamation auction – it had been lying out in a yard exposed to the elements for years,” says Molly. “I only used the roughest pieces.”

The main downstairs space is a soaring vault of a room, the floor of light travertine marble. At the west end stands perhaps the most lovely piece in the house, a Louis Seize desk which once stood in Macroom Castle in County Cork. Above it hangs a large ornate gilt looking glass just made for the spot.

To the right of the desk, on the north wall, is an almost equally impressive 18thcentury Italian walnut commode and above it a School of Claude landscape. To its left, a high, busy bookcase with reading ranging from Walter Scott via Mitford and E.F. Benson to Len Deighton – plus, as one might expect, extensive tomes on art, history and design. High above, the lighting is provided by an old 12-point chandelier – it’s original brass now softened by age – and small, unobtrusive, modern spotlights.

“We entertain a great deal and this really is the perfect space for a party,” she says. “It doesn’t matter how many people we have crowded in here, all the noise and smoke, if any, is lost high above.”

At the end of the main space, beneath the master bedroom, sofas gather round a wood-burning stove in a fireplace built from slim, reclaimed French bricks and topped with a reclaimed bressumer beam. A pair of elegant Adam brackets provide a candlelit intimacy and two more lovely landscapes adorn the walls.

The kitchen has been created from both space which was part of the main barn and from an area which was once little more than a corrugated iron outshot tacked onto the side of the main structure. Some of the beams that now support the bathroom above started life in the now-demolished barns, but others are a little more artful – flitch beams and RSJs which have been beautifully disguised as oak by Benenden craftsman Adrian Stephenson.

In the centre of the kitchen stands an old butcher’s block but the star of the show is an aged, and much-distressed, Irish dresser, a venerable home for the latest acquisition – a Victorian Harlequin dinner service.

“I decided to get rid of my blue and white – the Harlequin is so much more fun,” says Molly. “Not a single plate is the same and even the most expensive was only £7.”

Kitchen cupboards have also been painted by Adrian Stephenson and depict the four seasons. The bulk of an Aga would have taken up too much valuable space so Molly opted for a neater but equally effective oil-fired Rayburn, on which you can cook from cold in 15 minutes. Above, a selection of ancestors gaze down on culinary proceedings.

Upstairs on the landing and over the bedroom door is a portrait of Catherine of Braganza by Lely. Inside the glass door are the master bedroom and bathroom, the latter virtually built around a magnificent 17th century oak chest. Downstairs are two further bedrooms and a bathroom.

The barn stands in 23 acres of keep-sheep and a modest garden. Molly has also planted a lovely mixed orchard which now supplies her, when it feels so inclined, with apples, plums, damsons, pears, quinces, greengages, apricots, cherries and medlars. Behind the latest project – a summerhouse built entirely from leftover oakand tiles from the original site – is a vegetable garden literally brimming with produce.

It has been a long haul from moving the livestock out of the barn and the builders in, but she is quietly pleased with the result.

“My children don’t live here day to day but they all love the place,” she says. “And you know, I think the greatest compliment I’ve had has come from my younger daughter. She asked me if, when she buys her first London flat, I would design it for her.”