“Then there’s the section at the end where this baby grows out of the centre of the stadium,” he explains, wide-eyed. “And Danny wanted to use In Dulci Jubilo, so I made a new version of that.

“And there are all these people running around unveiling this… thing,” he continues. “And the very end section is a brand new piece, which is basically a piano and a big bell crescendo, and the lights come up and this giant baby which is supposed to represent the Olympic spirit grows out of the centre of the stadium and it ends with a big crash and lights.” Oldfield, an avuncular man with shaggy hair and a pocket full of Amber Leaf rolling tobacco, seems unfazed by the prospect of standing beneath a 23-ton bell marshalling musical proceedings for an 11-minute celebration of the NHS. But, since his involvement has been a well-kept secret for over a year, he could just be relieved that he’s finally able to talk about it.

Overcoming his fears about the weather, Oldfield is finally returning to the country that made him a star via Tubular Bells, the groundbreaking, 18million-selling 1973 album he recorded when he was 19. He’s coming home, to play his biggest concert ever.

Oldfield, a Reading-born, 59-year-old father of nine, and full-time resident of Nassau, left the UK under a crotchety cloud when the smoking ban, profusion of CCTV cameras and petty laws all got too much for him. “I read about a chap getting a ticket for eating a KitKat while driving! It’s like being at prep school!” he fumes. A lifelong speed freak and qualified pilot, he remains furious about his homeland’s “ridiculous” insistence on crash helmets for moped riders. But even that couldn’t dim his enthusiasm for the Olympics.

“What can I say?” is the smiling Oldfield line. “The Olympics is the project of a lifetime.”

Oldfield is a sanguine, mellow chap. Many of the “legends” surrounding his 40-year career are either untrue, or funnier in the telling. No, he’s not a Scientologist but he does practise, daily, transcendental meditation with the same dedication that he famously brought to bear on the dementedly intense recording of Tubular Bells. (The teenager played upwards of 20 instruments himself, pioneering new recording methods that became cornerstones of progressive rock.)

Yes, he is on good terms these days with Richard Branson, whose Virgin empire – and fledgling record-label – was kick-started by Tubular Bells’ success, and who Oldfield subsequently sued for royalties. But yes, he did embed his 13th album, 1990’s Amarok, with a Morse code message that spelt out “F--- off RB”.

No, he no longer has — as he said three years ago — no friends, only lawyers. An improving relationship with the mothers of his older children has helped there, and his legal dispute with Noel Gallagher is a distant memory. The one-time Oasis leader bought Oldfield’s house in Ibiza, then successfully sued him after he discovered part of the property was falling into the Mediterranean.

“I had about eight lawyers, now I have three, and I did pick up a new one for the Olympics. Hey, things are looking up!” he beams. “The day I have no lawyers, I’ll be a happy man.” His two sons, Jake, eight, and Eugene, four — his children by wife Fanny, whom he met in Ibiza and who is 24 years his junior — tumble about in their pants, begging dad to splash into the swimming pool with them. Normally Oldfield rises before dawn, working on music either here or in the other studio up the hill in his house. Current projects: the remastering of his back catalogue, a new compilation (Two Sides), and “one of the few things I’ve not done — a rock album”.

He mentions that one of the songs on the latter references domestic violence, “which I experienced a long time ago”. Later that afternoon, he explains what he meant by that. For decades Oldfield has been described as a reluctant rock star. In the Seventies, he shrunk from the bewildering and unexpected success of Tubular Bells. He hated publicity, was loath to tour. He even found it difficult driving into London. This was usually ascribed to, and dismissed as, either hippy nonconformism, or drugs.

Pressed on the subject now, he says, falteringly, “well, I think I was born with a sensitivity to any kind of stimulus. Then, um, a very disturbing childhood with my mother being, em, ahem, mentally disturbed. And my father as well, being a doctor, trying to cure her. But you’re not allowed to treat your own family. So there were doctors and hospitals and ambulances. There was fighting, there was violence.”

His mother Maureen, a Catholic nurse from Munster, was herself the product of a disturbed childhood. Her father had fought in the First World War, and came home traumatised. His mental health wasn’t helped by the Irish War of Independence and the sense that he was “hated by his own countrymen for having served in the British army”. She escaped to the UK and married Oldfield’s father, a Protestant. She was ostracised by her family.

“And that all built up into this terrible mental anguish,” Oldfield explains. “Which these days you would go and see a psychotherapist for, probably for the rest of your life.” At the age of 40, Maureen gave birth to a child with mental disabilities, who only lived for a year. “Then,” Oldfield sighs, “she had a hysterectomy. She couldn’t cope, became addicted to tranquillisers.” His mother died in the Seventies. But his father is 89 and lives in Germany. Oldfield senior and junior have discussed these events. But has he told him about the new song?

“What’s the point? It was a long time ago. He explained the frustrations he felt — if you’re a physician, your whole career, your calling, is to make people better. If you can’t, it’s soul-destroying, frustrating. We’re not talking about one week — we’re talking about years and years and years of it.” Little wonder that young Mike Oldfield immersed himself in music and hit the road as soon as he could. For this gifted but troubled teenager, making the all-instrumental Tubular Bells as a one-man band was the best therapy imaginable.

He has been in the Bahamas for four years, and is now the proud and grateful owner of a Bahamian resident’s card. This follows a variety of homes in southern England, and stints in Majorca and Ibiza (where, he admits, the Nineties hedonistic lifestyle almost got the better of him). It’s the longest he’s been in one place for years. Why?

Oldfield pauses and rolls another Amber Leaf, a consignment of which has been brought out from the UK by his publicist. “I don’t like being cold,” he finally says, eyes twinkling. “I went to Ibiza, then to my horror I discovered it was cold in winter. Then I tried Majorca, same thing there. Then I lived in Monaco for nearly a year. Oh, and Switzerland,” he suddenly remembers. “Then I was sitting in Monaco and this chap turned up with a brochure for the Grand Bahama Yacht Club, which is on the big island to the north. And I just booked a flight over to have a look. And it was lovely!

“So,” he continues, “I bought a house there, and guess what? It got cold in the winter! So we thought, let’s try Nassau — which gets cool but not, like, cold.” Was tax efficiency a motive? “It’s a factor, of course it is, yes. I know it’s a dirty word in Blighty… But that’s not the primary reason. Look!” he gestures at the view again. “It’s nothing to

do with money. You can’t buy that.” Actually, you can, as Oldfield did from an old expat family who were in the insurance business. But no matter. “To be able to come out of my room in the morning, it’s a beautiful sunny day, hop on my jet ski, I’m off in two minutes, out there – it’s paradise. Nothing to do with tax.

“You drive around inland, and you see England like it used to be in the Fifties. Kids going to school, they’ve got their uniform on, they’re happy, they can walk around the streets. People are out and about, doing things, they’re not rushing. There’s not policemen everywhere, censoring you; there’s not cameras everywhere, watching you.”

Oldfield hasn’t lived in a city since a brief stint in Tottenham, north London, in the early Seventies, where he painstakingly recorded the demos for Tubular Bells on clapped-out old recording kit. And even the slight “styling” he’s had to endure for today’s photo shoot is making him uncomfortable. “I haven’t worn a pair of long trousers for four years. My legs are suffering today.”

You can see why Danny Boyle’s vision of England’s green and pleasant land might have appealed to Oldfield. Indeed, at one point in their year-long discussions, Boyle had Oldfield and his band standing atop his recreation of Glastonbury Tor at the other end of the Olympic Stadium. In the end, Oldfield was replaced by an oak tree. “And I think I’m happier under the big bell.” And why, conversely, did Boyle want Oldfield? The musician is the first to admit he wasn’t the most obvious choice. “I expect half the audience will be going, 'what the heck?’ And the other half will be going 'yeah!’ And a lot will be going, 'who’s that?’”

Boyle filled him in during a meeting last year here in the studio. Boyle flew out on the morning flight from London, spent the afternoon with Oldfield, then took another nine-hour flight back in the evening. He played Oldfield a mock-up video of a section of the embryonic opening ceremony. He’d used a large part of a performance, titled Tubular Bells III, that the songwriter had staged in Horse Guards Parade in 1998. “Typically, it bucketed down with rain,” remembers Oldfield. “And typically, the British decided, 'well, to hell with this, we’re gonna have fun anyway.’ And it turned out to be a raging success.” Fans “were splashing about in the puddles”. Even Branson was “soaked, his hair all covered in rain. Everyone was happy. And the video of it was on YouTube and Danny had obviously come across it, and thought there was something that could be extended and developed and used in his vision of this section of the opening ceremony.”

Boyle explained that the portion in question was to celebrate the NHS, which he’d storyboarded into a narrative that “became a bit Dickensian. I was sitting there watching this, and it all seemed to me so magical. And I trusted him because I’m a tremendous fan of his films,” he nods. “I thought he would be able to pull it off. And I said straight away, 'count me in’.” Oldfield is a lifelong solo operator and canny curator of his own back catalogue. But his enthusiasm even withstood subsequent interfering from Boyle, which included the eventual handing over of finished pieces to the ceremony’s musical directors, Underworld, for remixing and mastering at London’s Abbey Road studios.

“Danny suggested a swing version of Tubular Bells,” says Oldfield, his eyebrows rising just a little. “He sent me a Benny Goodman track… At first I thought, 'you can’t, no.’ Then I started playing around with the sequences and mocking something up and thought, 'it really does work, yes.’ It just flowed from start to finish.” And yet. Aside from Oldfield’s proven ability to conjure performance magic in the rain, on what musical basis did Boyle hire him? It’s easy to see why Gary Barlow was enlisted for the Jubilee. One understands the all-star line-up of the closing ceremony. But Oldfield — a couple of hit singles (Moonlight Shadow, In Dulci Jubilo), one huge album (Tubular Bells), one television theme (Blue Peter), one famous soundtrack (The Exorcist) — is a less obvious choice.

“Well,” smiles Oldfield, “you’ll have to ask him, really.” But he’s not allowed to speak. I’ve tried. “Well, let me think what I would hope he’d say then… First of all, somebody who’s not an idiot and is not going to screw it up. Maybe he thinks, 'he’s a man who can deliver.’ You can’t give a task like that to someone who’s going to, I don’t know, turn up drunk and be rude to everybody. That’s probably why he wanted to come and meet me — to make sure I wasn’t going to be an idiot and ruin it all.”

But what was the musical thinking? “The bell, I suppose,” Oldfield shrugs. “If you think of music and bells in England, you think of me, don’t you?” With Pink Floyd’s The Division Bell album a distant second? “Oh, way second!” he chuckles. “I’d never even dream of that! No, they’re moon, aren’t they?”

Four weeks later, Mike Oldfield and family have arrived in the UK — “it was raining!” — and he’s fresh from his first visit to the Olympic Park.

“Luckily we went on a taxi bike — Virgin Limobikes, they call them,” he says, tickled by the reminder of the empire he helped found all those years ago. “I think it’s the only involvement Virgin will have, actually.” He’s also just heard the news that Branson is interested in buying back the Virgin record label. In which eventuality, might there be a place for Oldfield at his old friend’s side? “Well, I’m not with Virgin anymore but that was my first thought — aargh!” he says in Harry Secombe-like exclamation. “I don’t want to be back there!”

The Olympic Stadium, he reports, was a picture of “total organisation” during the initial rehearsals. “The place has a very welcoming atmosphere. You can feel all the energy that’s gone into the building of it over these months and years. It’s stunning. I was bowled over by it.” He was, though, “slightly alarmed” when he heard of the last-minute cut, reportedly necessitated by security and transport issues, of 30 minutes to the running order. “A little tiny bell at the back of my mind did ring. But I’m in hourly contact with everybody there. So I would know by now if I’d got the chop.” And what of the big bell?

“Oh, fantastic. My first thought, as you can imagine, was, 'I want to ring it.’” It’s all a long way from Mike Oldfield’s first heel-dragging live performance of the album that bought him those boats. In 1973, John Peel was an enthusiastic champion of Tubular Bells, calling it “entirely one of the most impressive LPs I’ve had the chance to play on the radio. A really remarkable record from Mike Oldfield.” But Richard Branson wanted to rocket-power his fledgling label and its first-ever album release by having Oldfield perform at London’s Queen Elizabeth Hall.

Oldfield, shy and nervous and probably stoned, was reluctant. In the end, Branson had to offer him a gift. What would persuade him to get on stage? Oldfield, then penniless, considered his £40 Mini that could only manage 35mph. Then he considered Branson’s Bentley. He chanced his arm and asked for the car. Branson duly handed it over. “It was better than my Mini!” laughs Oldfield.

And what inducements did he get from Danny Boyle to leave his Caribbean idyll and perform in rainy east London? “Oh, nothing. That was a long time ago. I was only 19.” So he’s performing for free? “Oh, yes,” he beams through a puff of smoke. “Sure. It’s just a tremendous honour. I’m proud to be there, part of the Olympics. Very proud.”

The compilation 'Two Sides’, the 6-disc set 'Mike Oldfield: Classic Album Selection’ and 'Isles Of Wonder: Music for the Opening Ceremony of the London 2012 Olympic Games’ are all available now

This article also appeared in SEVEN magazine, free with the Sunday Telegraph. Follow SEVEN on Twitter @TelegraphSeven