The walls are dazzling white; spanning four storeys it rises like a solitary skyscraper from the pristine landscape of one of the west coast’s smallest islands.

Wild in winter when it’s lashed by fierce storms and howling wind, on warm summer days Inch Kenneth House glistens like a diamond against an emerald carpet of grass and topaz blue skies.

To reach it requires a short – sometimes turbulent – boat trip from Mull. For those who make the journey, the tiny island of Inch Kenneth rewards them with a landscape as wild and unspoiled as in 1773 when intrepid pair Dr Samuel Johnson and James Boswell paid a visit.

Remote, secluded – planning is essential to avoid running out of fuel for the fire, or fresh supplies for the table – it is perhaps the last place you’d imagine a young upper crust London debutante with Nazi sympathies might wish to be.

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Yet for almost 30 years, the gleaming white walls of Inch Kenneth House was a precious bolthole home for one of Britain’s most intriguing families.

And, 75 years ago this summer, it would become the final destination for one of its most controversial members, a Nazi sympathiser said to have hung a swastika from its flagpole, and apparently tried to signal to German u-boats from the beach using her bicycle lamp.

The glamorous Mitford sisters’ looks, talents and often extreme, differing political views fascinated London society and beyond during the 1930s and 1940s: Nancy, Pamela, Diana, Unity, Jessica, and Deborah were the ‘It Girls’ of their age.

But whereas Diana denounced her privileged life and turned to communism, Unity and Deborah became high-profile supporters of Hitler and regulars among Munich and Berlin’s Nazi elite.

While Deborah married British Union of Fascists leader, Sir Oswald Mosley – a ceremony performed in the dining room of Nazi propaganda chief Joseph Goebbles – Unity, was besotted with Hitler. She moved to Munich, spoke fluent German, and greeted people with a Nazi salute and "Heil Hitler".

The fourth of the six ‘mad, mad Mitford sisters', she told friends that “the greatest moment in my life was sitting at Hitler's feet and having him stroke my hair”.

The Herald: English writer Jessica Mitford, at the age of six, reading with her nine-year-old sister Unity in the garden of Asthall Manor, their home in Oxfordshire, 1923. (Photo by Evening Standard/Getty Images).English writer Jessica Mitford, at the age of six, reading with her nine-year-old sister Unity in the garden of Asthall Manor, their home in Oxfordshire, 1923. (Photo by Evening Standard/Getty Images). (Image: free)

In return, Hitler praised her to German newspapers as “a perfect specimen of Aryan womanhood”, bestowing upon her the high honour of the gold Nazi party badge.

They became so close, that British newspapers suggested – mistakenly – that marriage might beckon.

But as war grew closer and under increasing pressure to decide where her true loyalties lay, Unity became increasingly tortured by the thought of having to choose between Britain or Germany.

On September 3, 1939, as war was confirmed, she retreated to a quiet garden in Munich and used the pearl-handled pistol Hitler had given her for protection to shoot herself in the head.

Years earlier, in the early 1930s, Inch Kenneth island with its farm cottage, livestock and large house had been owned by Sir Harold Boulton, writer of the words to the Skye Boat Song.

Before his death in 1935, the house overlooking the beach had been extended creating an eclectic mix of part Highland castle, part country house, part art deco mansion, it featured up to 10 bedrooms, a private chapel, and bold front ‘bow’ to make the most of its spectacular views.

With war on the horizon, the Mitford sisters’ parents, Lord and Lady Redesdale, snapped it up.

And it was at Inch Kenneth where, fearful of being too close to London, most of the family gathered, including sister Nancy and her parents, on the fateful day Unity tried to take her life.The Herald: Inch KennethInch Kenneth (Image: FREE)

That she lived was a miracle. In Germany, Hitler paid for Unity’s medical care for months before funding her transport to England in 1940, the inoperable bullet still deep in her brain.

But the injury changed her character.

“She was just about recognisable as the person we knew, but the person we knew wasn't there anymore,” said her sister Deborah, Duchess of Devonshire, in one interview. “My sister was incontinent; my mother washed her sheets every night and would hang them out to dry.”

As war raged, Inch Kenneth and the shimmering white house became a sanctuary for the Mitfords and kept Unity well away from prying eyes and the London press who may well have revelled in her misery.

For Unity’s behaviour was erratic. Speaking in a short film of Inch Kenneth House in 2010, her sister told how she had delusions that she was a clergyman and would dress up to take a pretend service in the island’s ruined chapel, amid ancient gravestones.

“It was so surreal, she’d forget the words she meant to say and stomped off in a rage. It was incredibly difficult,” she added. “It was very sad.”

In the house, she blared Nazi marching band music from her gramophone, and devoured Nazi books including a copy of Mein Kampf signed by Hitler and antiSemitic paper, Der Sturmer.

On outings to Mull, she was known to wear a swastika armband – behaviour tolerated by islanders but which still fuelled rumours that she hoped to summon passing U-boats using her bike lamp, and of welcoming the Kriegsmarine to the island she’d come to consider her own Nazi outpost.

In 1948 the bullet moved. As her health deteriorated she was rushed – as fast as possible given island’s remoteness – to hospital in Oban where she died on May 28, 1948.

Her mother, who had committed her life to caring for Unity, remained at Inch Kenneth until her health also failed.

She died there 60 years ago in May 1963, almost exactly 15 years to the day after Unity’s death.

The house was eventually bought by artist Yvonne Barlow, granddaughter of Sir Charles Darwin, and her husband, Andrew, a hospital doctor, for use as a holiday retreat.

Today there is nothing on the outside of Inch Kenneth House to show of its one-time occupants.

Inside, however, is a different story: chairs, tables, beds and the piano where the Mitfords and their guests once gathered, remain.

Now passed into the hands of siblings, Dr Claire Barlow, and her brother Martin, in recent weeks it has been a scene of activity once more, as a extensive repairs which it’s hoped will ensure the house remains weatherproof against the wildest Inner Hebridean blasts, reach a conclusion.

Dr Barlow remembers arriving at Inch Kenneth as an 11-year-old as her parents viewed it for the first time and almost didn’t bother buying it.

“My parents were in London and had been looking to buy a house in the countryside, and the estate agent sent back details of this island – not at all what they were thinking about,” she says. “Dad had a few days holiday, thought they would go for a look, but they weren’t really expecting to buy an island.

“My father arranged to be brought over on a little boat, it was stormy and windy and went to the house and it was literally dripping and green with mould inside.

“My parents thought ‘this is too much’.”

However, they returned for a second look on a sunny day – and fell for the island, despite the house.

They paid just £25,000 for the entire island.

The family patched up the house, ripped out the Mitfords’ ‘chintzy’ curtains and frills and replaced it with a simpler style while retaining much of the famous family’s furniture.

Eventually, there are hopes it might fall under the care of a charitable trust, and become a precious, unspoiled retreat for artists and writers.

“It would be nice if, when the time comes, we could sell it to a trust that would respect the quiet and special nature of the place,” adds Dr Barlow.

Its unusual history, however, remains a curiosity to those few visitors who make their way to the remote island.

“Occasionally people will want to come and look at the house or want to be taken around,” she adds.

“I can be sitting inside and there are people come and look through the kitchen window.”