In Wallis's footsteps: The holiday home by royal appointment

The Moulin de la Tuilerie is a paradise of warm stones and wooded slopes: an image of France at its most profonde. The 18th-century mill beside a chattering stream is also a paradox wrapped in a contradiction. It is a rural Eden which stands 35km from the Eiffel Tower. It is a corner of deepest France which will be forever England.

For almost two decades, the Moulin was the retreat of Britain's king over the water and his forbidden American bride. Here, from 1952 to the late 1960s, the Duke and Duchess of Windsor – "David and Wallis" to their closest friends – entertained, casually or royally. Their house guests included, among others, Cecil Beaton, Richard Burton, Elizabeth Taylor and Marlene Dietrich.

Here, the Windsors, the most photographed couple of their era, also liked to pretend that they were ordinary people. "David", the present Queen's uncle, gardened in muddy, baggy trousers and crumpled tweed jackets – as is every Englishman's right. Wallis played mummy to her surrogate family of pug dogs.

The former King Edward VIII (the only British monarch to abdicate in modern times) also had a more formal house in the Bois de Boulogne, which was let to him for a peppercorn rent by the city of Paris. The Moulin at Gif-sur-Yvette, a little to the south of Versailles, was the only house that the Windsors owned. Wallis once described it as "our only real home".

From July, the Moulin de la Tuilerie can be anyone's home – for a weekend or a week or a fortnight. The mill which was once the Windsors' pride and joy is to be the first cross-Channel venture of The Landmark Trust, the British charity which buys and restores historic buildings and lets them to weekenders and holidaymakers.

Landmark France, will, for the most part, be a partnership with the agency which protects the French coastline, the Conservatoire du Littoral. Plans are well advanced for Landmark – at the Conservatoire's invitation – to restore and let a series of abandoned, historic buildings along the French coast, starting with a sardinery on an island off Douarnenez in Brittany and a fort on an island off La Rochelle. These buildings should be ready by 2012.

However, Landmark's first cross-Channel excursion – to be formally announced today – is to be one of the charity's most spectacular sites. Holidaymakers will be able to take either the main mill house at Gif (which sleeps 12) or the two stone outbuildings converted by the Windsors (which sleep four or two).

Caroline Stanford, Landmark's historian and assistant director of Landmark France, said: "The Moulin triumphantly meets all our criteria for a Landmark site. It is a beautiful place in itself. The buildings have the simple, elegant charm of rural France – buildings with soul and purpose, made from local materials which blend perfectly into their surroundings.

"But the mill is also deeply entwined with one of the key moments in British 20th century history ... and not just British history. The Windsors were an important part of Paris society in the 1950s and 1960s. They also had a great influence on the style of the period. And because Wallis was American, they remain iconic figures in the US to this day."

King Edward VIII abdicated on 10 December 1936 after less than 11 months on the throne. The British, and Dominion, governments had made it clear that they would not accept Wallis Simpson, his twice-divorced, American, former mistress, as the Queen or even as the Royal Consort. Faced with a triangular choice between his throne, a constitutional crisis or "the woman I love", Edward VIII – always known to the Royal family as David – chose Wallis.

The couple spent the rest of their lives in exile from Britain, symbols of romance and style to some; wrong-headed, immature, irritating socialites to others. The Royal family always refused to acknowledge Wallis as an HRH. Edward's reputation never recovered from his playing footsie with Adolf Hitler, who cleverly offered Wallis full state honours to persuade the couple to visit in October 1937, soon after their marriage.

After the war, the Windsors accepted an invitation from the French government to settle, tax-free, in Paris. They bought the mill in 1952 from the French painter Etienne Drian to escape their grander but too-public house in the Bois de Boulogne. Most weekends, "David" and Wallis would drive the 30 minutes from Paris in his Daimler. The Duchess's luggage, pugs and two maids would follow in her light blue Cadillac station-wagon.

Externally, the buildings today remain almost unchanged since the Duke and Duchess's time: an island of rural charm in the green Chevreuse valley and national park at the edge of, but untouched by, the south western sprawl of the Parisian suburbs. The gardens straddling the stream still have the outline which was imposed – and sometimes personally hewn and dug – by the Duke. He spent much of his time at the mill "looking crumpled and happy", according to one guest. His beloved beds of showy flowers, which make the grounds look like an impressionist painting in contemporary photographs, have long since become lawns.

"It is a very tranquil place," the Duke once said, "where one can garden as one should in old clothes, with one's hands among familiar plants." The royal habit of describing oneself as "one" goes back at least two generations, it seems.

In her 1987 book, The Windsor Style, Suzy Menkes has a chapter on life at the Moulin. She says that the Duke employed five gardeners, two of them Spanish, two Alsatian and one French. "As the Duke's German is sort of better than his French, he likes to talk German with them," the Duchess is quoted as saying.

The graves of several generations of Windsor pug dogs – Trooper, Disraeli, Imp, Davy Crockett – can still be found among the trees and boulders of the hill that overlooks the house. This was known as "Cardiac Hill" to the Duke, who would force his overweight guests to climb to the crest.

At the end of the garden is a round stone hut, still divided into the original His and Hers changing rooms designed for the Duke and Duchess (blue stripes for him; red stripes for her).

Inside the main mill house, much of the original decoration was stripped out by the Lebanese millionaire who owned the house in the 1980s and 1990s. One amusing vestige remains.

The Duchess had a mural painted on the main wall of the upstairs reception room as a wry commentary on the poor treatment that she believed that she had received at the hands of the British establishment. The mural, as clear today as the day it was painted, shows a water mill wheel entwined with the words: "I'm not the miller's daughter but I've been through the mill."

To know how the rest of the interior looked in the 1950s and 1960s, you need to use your imagination or to consult the many pictures that were taken at the time. One large wall was occupied with a giant map of the world, marked with the Duke's 150,000 miles of Imperial journeys as Prince of Wales in the 1920s. Another carried a frame containing the regimental buttons of every British unit which fought in the trenches in the 1914-18 war – a war in which the young David had insisted on serving, briefly, in the front line. He was even mentioned in dispatches.

The interior décor was, judging by photographs, garish, verging on the dazzlingly ugly. "It was very bright with patterned carpets, lots of apricot, and really more Palm Beach than English or French," said Diana Mosley (nee Mitford), the wife of the British fascist leader, Sir Oswald, an unrepentant Nazi fellow-traveller and frequent visitor at Gif in the 1950s. The American interior decorator Billy Baldwin says in the Suzy Menkes book: "Most of the mill was awfully tacky but that's what Wallis had – tacky southern taste, much too overdone, much too elaborate and no real charm."

The upper northern wing of the house consists of the former, separate apartments of the Duke and Duchess (hers much grander than his). Although only the walls remain, it is easy to imagine the Duchess lolling in a tub in her stunning bathroom with picture window views of the countryside on three sides. The Duke had a tiny bedroom with upstairs bathroom, where, preferring to shower, he kept his books and papers in the bath.

The Landmark trust is in the process of restoring and refurnishing the mill's interior in comfortable appropriate style but will not (mercifully) attempt to recapture the interior Windsor look. The charity, founded in 1965, owns or manages 182 properties in the United Kingdom. It already has four " Landmarks" in Italy, which have connections with the British poets Shelley, Keats and Browning. In 2007, Landmark was approached by the Conservatoire du Littoral and asked to extend its work to France.

The Conservatoire was impressed by Landmark's work in Britain. It wanted an experienced partner to help to rescue scores of disaffected, but potentially stunning, buildings along the French coastline. The Landmark Trust's Director, Peter Pearce, told The Independent: "In many ways, we share the same values and aims as the Conservatoire. They have an obligation to preserve the beauty of the French coastline. We have experience, unique in the world, in identifying and restoring threatened buildings of historic value and giving them a new life by making them available for weekenders or holidaymakers. It seemed like a partnership made in heaven."

The Conservatoire will provide around 80 per cent of the funds for the restoration of French coastal buildings. The rest will come from sponsorship and appeals in France.

The French " Landmarks" will be let to both British and French holidaymakers and – it is hoped – inspire more cross-Channel visitors to stay in the charity's properties in the UK.

Work has now progressed to the point that Landmark has created a wholly French clone, Landmark France, which is non-profit-making like the UK parent. Two French coastal "Landmarks" are under development and should be ready for letting in the next couple of years. One will be based in old sardine fishery offices on an island off the Breton coast at Douarnanez, just south of Brest. There are plenty of British historical connections, as Caroline Stanford, Landmark's historian points out. Douarnenez was blockaded by the British fleet in Napoleonic times and was for centuries a base from which French privateers raided British shipping.

The second coastal "Landmark" in France will be the Ile Madame, an 18th- and 19th-century fortress off La Rochelle, built to protect France from ... guess who. A score of other French coastal " Landmarks" will follow.

The Windsors' mill – which falls outside the scope of the partnership with the Conservatoire du Littoral – became available just as Landmark France was taking shape. "It is, we hope, the perfect property to give a lift-off to the French venture," said Caroline Stanford. "We expect international interest and also an income to help fund development of our other French projects once it is ready to let from July."

There are three buildings on the site: the main mill sleeping 12, and the annexes Le Célibataire (The Bachelor Pad) sleeping two and La Maison des Amis (The Friends' House) sleeping four. They will be available separately or all together but each building must be let as a complete unit. Although details have not yet been finalised, Landmark says that holidaymakers or weekenders who take the whole of one, or more, of the three buildings on the site for at least three nights should expect to pay about £50 per day per head.

The Moulin de la Tuilerie had been empty and disused for four years when it was taken over by a British investment company in partnership with a Briton who had moved to France, Patrick Deedes.

"I was looking for a change of direction and wanted to restore a very special property in France," Mr Deedes, 50, told The Independent. "We looked at more than 80 places before we stumbled on this. It had been empty for four years and was in, well, quite a state but the basic buildings were still fine."

Last year, Mr Deedes and the investment company which owns the Moulin reached an agreement with Landmark to complete the restoration and manage the buildings from this summer.

Mr Deedes, his wife, Isabelle, a former model, and their two daughters, aged nine and five, live in the Moulin's gatehouse. Thereby hangs another tale, which links the mill to a second generation of forbidden royal romance.

Isabelle Deedes is the daughter of Group Captain Peter Townsend, the RAF officer and former equerry to King George VI who was refused permission to marry Princess Margaret in the 1950s because he was a divorcé. Group Captain Townsend later moved to France and fell in love with a Belgian woman – Isabelle's mother. He was a frequent visitor at the Moulin in the Windsors' time. They even named one of their pugs after him.

"This was pure coincidence," said Mr Deedes. "Isabelle was a little doubtful at first, because of the link with her father ... But we decided to take the plunge. We are very pleased that we did. It is very special place. Even without the history, it is a special place. The historical connections make it an extraordinary place." A corner of a foreign field which will remain forever ...

Strolling around the grounds where the Duke of Windsor once laboured, and gave orders to his Spanish gardeners in German, we spotted a small white object lying in a narrow watercourse. It turned out to be a ball belonging to the Deedes' daughters. It was marked with the red and white cross of St George and carried a single word: "England".

Official residence: The Windsors in Paris

The official home of the Duke and Duchess of Windsor from 1950 was a 19th-century villa at 4, Rue du Champ d'Entraînement in the Bois de Boulogne, on the western outskirts of Paris. The house, belonging to the Paris town hall, was given to the Windsors at a nominal rent to encourage them to move to France.

They never liked the villa much. It was not theirs. It was too public. They felt, according to friends, like animals in a gilded zoo. Although they entertained, very formally, in the Paris house, they spent every weekend and every summer in their "only real home", Le Moulin de la Tuilerie.

When the Duchess died in 1986, 4, Rue du Champ d'Entraînement was leased for 50 years to Mohammed al Fayed, the owner of Harrods. In 1997, he irritated the Royal family, and the Paris Town Hall, by selling off its contents, including the remaining Windsor memorabilia, at auction.

On the morning before their fatal car crash in Paris in August 1997, Mr Al Fayed's son, Dodi, and Diana, Princess of Wales, visited the old Windsor villa in Paris. Mr Al Fayed has since suggested that, had they lived, they would have made it their home. The Princess's friends have disputed this.

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