Saying goodbye to his father at Holt Railway Station is Sir James Dyson's "most painful memory" of growing up in Norfolk, the billionaire has revealed.

Speaking exclusively to this newspaper, Sir James, 75, has told of the day his father Alec Dyson left for London to undergo cancer treatment.

Sir James was nine at the time. "It was the last time we ever saw him," he said. "His brave cheerfulness chokes me when I recall the scene."

Sir James, who was born in Cromer, has just visited Gresham's School in Holt to officially open the £18.75m Dyson STEAM Building, which he and his wife Deirdre paid for as a thank you to his former school.

His father had been a teacher of classics at Gresham's, and Sir James was allowed to continue his education there free of charge after Alec's death left this family without the means to pay for it.

This was down to the generosity the school's then headmaster, Logie Bruce-Lockhart, who taught the young Sir James valuable lessons that would go on to inform his career as an innovator and entrepreneur.

He said Mr Bruce-Lockhart's key mantra was to "throw yourself into everything".

Sir James said: "Logie – my late, great headmaster – was a fan of the individual.

"He believed that exam results were important, but so were other skills. I always enjoyed making things – model gliders and balsa-wood planes, including some with small diesel engines, and lead soldiers.

"I didn’t play with these or collect them but enjoyed using my father’s tools to make them, melting lead in a crucible and pouring the dangerous molten metal into moulds."

During his time at Gresham's from 1956 to 1965, Sir James said he tackled almost every non-academic pursuit on offer, including "bassoon playing, the Combined Cadet Force, acting and set designing in drama, running and rugger".

Despite the pain of his father's death and being born in an "age of austerity", Sir James said his childhood memories were "mostly very happy ones" in a landscape with plenty of space stretch his legs, both physically and figuratively.

He said: "At home, there was no television, never enough heating, no new toys. But it was an idyllic time.

"My father was head of classics at Gresham’s and my siblings and I, with the children of the other teachers, formed a kind of tribe."

Sir James said they lived a "Swallows and Amazons" existence, especially in school holidays when they had free run of the schoolgrounds, including the tennis courts and swimming pool.

He said: "Norfolk felt more remote than it does now. I remember my father teaching me to sail dinghies from Blakeney and on the Broads as well as waking up early to catch the spring tide down at Morston.

"Later, as a teenager, I used to run and run across the vast open spaces of the north Norfolk coast and didn’t think anything of going 10 miles or more.

"I have lifelong memories of running early in the morning or late at night through that hauntingly beautiful landscape. It was the first thing I knew I was good at, and it made me think that anything and everything was possible."

Starting with a 'ballbarrow' - a version of a wheelbarrow using a ball instead of a wheel, Sir James built one success on top of another, culminating in the bagless vacuum cleaners that are synonymous with is name.

His other products include the now ubiquitous Airblade hand dryer, and a hairdryer called the Supersonic which retails at £330. It quickly became a market leader after its 2016 release.

His career has not been without controversy - he was accused of hypocrisy for campaigning in favour of Brexit before the 2016 referendum, and then moving his company's headquarters from Wiltshire to Singapore less than three years later.

According to this year's Sunday Times Rich List he is now the UKs second richest person with an estimated net worth of £23 billion.