When he was five, Kevin Wheatcroft received an unusual birthday present from his parents: a bullet-pocked SS stormtrooper’s helmet. He had requested it especially.

The next year, at a car auction in Monte Carlo, he asked his multi-millionaire father for a Mercedes: the G4 that Hitler rode into the Sudetenland in 1938. Tom Wheatcroft refused to buy it and his son cried all the way home.

Kevin Wheatcroft is now 55, and according to the Sunday Times Rich List, worth £120 million. He lives in Leicestershire, where he looks after his late father’s property portfolio and oversees the management of Donington Park Racetrack and motor museum (which he also owns).

Tycoon: Kevin Wheatcroft, owner of the world's biggest collection of Nazi memorabilia reportedly worth in excess of £100million although no-one knows the true value

Forgotten army: The tycoon keeps uniforms form an era of history that many find too shocking to amire

The ruling passion of his life, though, is what he calls the Wheatcroft Collection — widely regarded as the world’s largest accumulation of German military vehicles and Nazi memorabilia.

The collection has largely been kept private, under heavy guard, in industrial buildings Wheatcroft owns near Market Harborough, or at his homes in Leicestershire, south-west France and south-west Germany. There is no official valuation, but some estimates put the worth at more than £100 million.

Among the internet tribes of World War II enthusiasts, the Wheatcroft Collection is spoken about as a near-mythical trove. Now he is guardedly opening it up to a wider audience, launching a rather creaky website and putting a handful of vehicles on display at his motor museum.

Wheatcroft’s father, Tom, a building site worker from Castle Donington, returned from World War II a hero. He also came back with a wife, Wheatcroft’s mother, Lenchen, whom he had first seen from a tank turret as he pulled into her village in Lower Saxony.

Tom, who died in 2009, made millions in the post-war building boom, then spent the rest of his life indulging his zeal for motor cars.

Exact figures are hard to come by, but the annual global turnover of the market for Nazi memorabilia is estimated to be in excess of £30 million. The trade is either banned or strictly regulated in Germany, France, Austria, Israel and Hungary. No major auction house will handle Nazi memorabilia and neither will eBay.

Aiming high: Mr Wheatcroft started his collection with a stromtrooper's helmet that his parents bought him for his fifth birthday and has built it into what is believed to be the world's biggest hauls of German military vehicles and Nazi memorabilia

Still, the business flourishes, with interest from buyers in Russia, America and the Middle East.

When I went to see the collection, Wheatcroft met me off the train at Market Harborough. ‘I want people to see this stuff,’ he told me. ‘There’s no better way to understand history. But I’m only one man and there’s so much of it.’

He recently purchased two more barns and a dozen shipping containers to house his collection. As we made our way into the first warehouse, he stood back for a moment, as if shocked by the scale of it all.

‘Every object has a story,’ Wheatcroft told me as we stepped over U-boat torpedoes and V2 rockets. He owns a squadron of 88 tanks — more than the Danish and Belgian armies combined. We stood beside a Panzer IV, patched with rust and freckled with bullet holes.

Wheatcroft scratched at the paintwork to reveal layers of colour: its current livery, the duck-egg blue of Christian Phalangists from the Lebanese civil war, the green of the Czech army who used the vehicles in the Sixties, and finally the original German taupe. The tank was abandoned in the Sinai desert until he shipped it home to Leicestershire. The value of his machines is dazzling. ‘The Panzer IV cost me $25,000. I’ve been offered two-and-a-half million for it.’

Trying to work out the value of the objects around me, I gave up somewhere north of £50 million. Wheatcroft has made a fortune, almost without realising it. ‘Everyone assumes I’m a spoilt rich kid who wants to indulge in these toys,’ he said. ‘It’s not like that at all. My dad supported me, but only when I could prove that the collection would work financially.’

Whiter than white: Mr Wheatcroft tries to avoid questions about why he keeps the collection as people often accuse him of being a Nazi himself. He says he likes the items because every one tells a story

In one of the warehouses, I spotted a dark wooden door, heavy iron bolts on one side.

‘That’s the door to Hitler’s cell in Landsberg Prison,’ he said. ‘Where he wrote Mein Kampf. I was in the area when the prison was being pulled down. I drove there, parked and watched the demolition.

‘At lunch, I followed the builders to the pub and bought them a round. I did it three days in a row and by the end I drove off with the door, some bricks and the iron bars from his cell.’

Near the door sat a trio of rusty wine racks. ‘They were Hitler’s. We pulled them out of the ruins of the Berghof [Hitler’s home in Berchtesgaden] in May 1989. The place was dynamited in ’52, but my friend and I climbed through the ruins of the garage and down air vents to get in.’

Later, I came across a massive bust of Hitler. ‘I have the largest collection of Hitler heads in the world,’ he said. ‘This one came from a ruined castle in Austria. I bought it from the town council.’

Wheatcroft’s huge, modern home sits behind high walls and heavy gates. A Krupp submarine deck gun stands sentry outside the back door. One outer wall is set with maroon half-moons of iron work, inlaid with runic symbols.

‘They were from the officers’ gates to Buchenwald [concentration camp],’ he told me in an offhand manner. ‘I’ve got replica gates to Auschwitz — [embellished with the words, Work Brings Freedom] Arbeit Macht Frei — over there.’

The immense, two-storey barn conversion behind his house wore fresh paint and shiny new locks. ‘I have to have strict rules,’ he said, ‘I don’t show many people the collection, because not many can understand the motives behind it, people don’t understand my values.’ He kept making tentative passes at the stigma attached to his obsession, as if baffled by those who might find his collection distasteful, yet desperately keen to defend himself, and it.

Mr Wheatcroft's father returned from the war a hero. He also returned with a wife, Kevin's mother, whom he had first seen from a tank turret as he pulled into her village in Lower Saxony

In-house: Mr Wheathouse keeps his most precious memorabilia in his own home but the collection is so large that he keeps hauls of items in various secure locations

The lower level housed the Mercedes G4 that Wheatcroft saw as a child in Monaco. ‘I cried and cried because my dad wouldn’t buy me this car. Now, almost 50 years later, I’ve finally got it.’

Upstairs, in a long, gabled hall were dozens of mannequins in Nazi uniform — Hitler Youth, SS officers, Wehrmacht. One wall was plastered with sketches by Hitler, Albert Speer and some rather good nudes by Göring’s chauffeur.

On cluttered tables sat a scale model of Hitler’s Kehlsteinhaus mountain eyrie, a twisted machine-gun from Rudolf Hess’s crashed Bf110 (in which he flew to Scotland), the commandant’s phone from Buchenwald, Enigma machines.

We were standing in front of signed photographs of Hitler and Göring.

‘I think I could give up everything else,’ he said, ‘the cars, the tanks, the guns, as long as I could still have Adolf and Hermann. They’re my real love.’

I asked whether Wheatcroft was worried about what people might read into his fascination with Nazism. ‘I try not to answer when people accuse me of being a Nazi,’ he said. ‘I tend to turn my back and leave them looking silly. I think that Hitler and Göring were such fascinating characters in so many ways. Hitler’s eye for quality was just extraordinary.

‘More than that, though, I want to preserve things. I want to show the next generation how it actually was. This collection is a memento for those who didn’t come back.’

His most treasured pieces are kept in his house. In the drawing room sat Eva Braun’s gramophone and record collection in a handsome walnut case. The cluttered snooker room housed a selection of Hitler’s furniture, picked up at a guesthouse in Linz

Famous faces: The collection includes busts of prominent Nazi figures, including numerous examples of Hitler himself. Mr Wheatcroft boasts he has the largest collection of Hitler heads in the world

‘The owner’s father’s dying wish had been that a certain room should be kept locked. I knew Hitler had lived there and finally persuaded him to open it and it was exactly as it had been when Hitler slept in the room. On top of the desk was a blotter covered in Hitler’s signatures in reverse, the drawers were full of signed copies of Mein Kampf. I bought it all. I sleep in the bed, though I’ve changed the mattress.’ A shy, conspiratorial smile.

In the galleried dining room was fugitive SS physician Josef Mengele’s grandfather clock, topped with a depressed-looking bear. ‘I had trouble getting that out of Argentina. I finally had it smuggled out as tractor parts going to the Massey-Ferguson factory in Coventry.’

By a spiral staircase, Wheatcroft paused beneath a full-length portrait of Hitler. ‘This was his favourite painting of himself, used for stamps and official reproductions.’ In an unexceptional bedroom, Wheatcroft reached into a cupboard and with careful hands pulled out Hitler’s white dress suit.

‘I was in Munich with a dealer,’ he said, showing me the tailor’s handwritten label: Reichsführer Adolf Hitler. ‘We had a call to visit a lawyer, who had some connection to Eva Braun.

‘In 1944, Braun had deposited a suitcase in a fireproof safe. He quoted me a price, contents unseen. The case was locked.

‘We drove to Hamburg and had a locksmith open it. Inside were two full sets of Hitler’s suits, two Sam Browne belts, two pairs of shoes, two bundles of love letters written by Hitler to Eva, two sketches of Eva naked, sunbathing, two self-propelling pencils. A pair of AH-monogrammed eyeglasses. A pair of monogrammed champagne flutes. A painting of a Vienna cityscape by Hitler that he must have given to Eva.

Mein Kampf: The famous and extremely controversial book that Hitler wrote while in prison

‘I was in a dream world. The greatest find of my collecting career. Now, it’s hard to know what to do with all the stuff. I feel I’m a caretaker until the next person comes along, but I must display it, I must get it out into the public.’

Many would question whether such artefacts ought to be preserved at all, let alone exhibited.

It is, perhaps, their very darkness that attracts collectors. In the conflicting narratives and counter-narratives of history, there is something satisfyingly simple about the evil of the Nazis.

The strange thing about my visit was not its weirdness, but its normality. I had expected a wild-eyed goose-stepper; instead I met a man wrestling with a hobby that became an obsession and was now a millstone.

Collecting was like a disease for him. If he was mad, it wasn’t the madness of the anti-Semite, rather the mania of the collector.