He may have been stepping into Brandon Routh’s shoes but Henry Cavill had to slip into Christopher Reeve’s suit. Well, maybe “slipped” is the wrong verb – by Cavill’s own admission, it wasn’t the most flattering of fits.

“It was a linen suit, and I wasn't in great shape. Linen doesn't look good when it hugs all the fatty bits. Don't try it, it's not worth it. I felt horrendous.”

Of course it probably didn’t help that the ill-fitting suit happened to be a replica of the most famous suit in the world, probably the most famous suit in history; the blue-and-red number created by Jerry Siegel and Joe Shuster in 1935, brought to life 40 years later by costume designer Yvonne Blake for the film that made a generation believe a man could fly, and invented the superhero blockbuster as we know it today.

No, this is a suit you want to look your best wearing, especially if you’re in the Hollywood Hills screen-testing for the biggest role in cinema, a role that has already escaped you once before. “Linen,” as another Boys’ Own icon might have muttered. “Why’d it have to be linen?”

It’s a good anecdote, filtering the last golden age of Hollywood through the lens of the modern industry. (Of course the suit’s material would now be archaic; of course it wouldn’t quite fit.) The situation is relatable – which of us haven’t donned a flashy new garment for a big occasion and duly reeled before the mirror – yet also delightfully exotic: Los Angeles; Reeve; Superman.

It’s good Henry Cavill, too. Light, self-deprecating, told with a ‘it could have happened to anyone’ deftness, except of course it couldn’t: not many of us find ourselves auditioning for the most iconic name in popular culture – even in someone else’s clothes.

And as you can see from our photoshoot, Henry Cavill looks damn good in a suit (at least the type where the pants are worn on the inside). Received wisdom decrees that famous people, really famous people, tend to appear smaller in the flesh, scaled down from the billboards and big screens.

When you start doing the big stunts with the big boys, the adrenaline does definitely spike a little bit

Cavill is bigger: north of 6ft, and with a build to make a wardrobe search for the nearest brick shithouse to cower behind. Your grandmother would describe him as a “strapping young fellow”, while your wife quietly slips her wedding ring into the nearest drawer. Never has a man looked quite so obviously Leading.

A cinematic star needs a cinematic setting – so we recruited the Shangri La penthouse at the Shard, and thus half of London sprawled out beyond gigantic panes of glass. We have gathered in the premierx suite of Europe’s tallest building to discuss Cavill’s role in Mission: Impossible – Fallout; or rather the little that Cavill can discuss about his role in Mission: Impossible – Fallout.

Refreshingly for a modern blockbuster – where spoilers are tossed into the first trailer, and the plot can be deciphered a month before general release – very little is known about the sixth installment of the M:I franchise. Naturally, it stars Tom Cruise as daredevil superspy Ethan Hunt, naturally there is a countdown to an imminent global catastrophe, and naturally a lot of vehicles will blow up.

Cavill is the headline addition to an ensemble cast that includes returning M:I alumni Simon Pegg, Rebecca Ferguson, Michelle Monaghan, and Ving Rhames – a veteran of the very first installment way back in 1996. (Cavill was 13.) Our man plays “primary antagonist” August Walker – a thrusting CIA agent whose methods clash with Hunt’s inexhaustible heroism. (Hunt can’t be much chill, although neither is Walker by the sound of things.)

“I'm forced upon Ethan's team by the director of the CIA. August Walker is a sledgehammer to Ethan's scalpel. He will get the job done no matter what. His MO is so different to Ethan's that naturally they don't get along at all. Walker has no problem with collateral damage,” notes Cavill with a certain fondness. “He's fine with it.”

Which is fortunate, as the trailer promises plenty of collateral will be duly damaged. Including the leading man: Tom Cruise broke his ankle chasing Cavill across the rooftops of London. (Fortunately for on-set harmony, the men were filming at the time.) Cruise, the utter pro, finished the take, but production was halted for several weeks.

Cavill spent the hiatus developing the character of Walker – and enjoying a little downtime. Every cloud… “I didn't break my ankle, so I got a holiday and my character got better!” he says cheerily. “Wasn't even a cloud: just silver lining!”

After such a mishap, it might seem prudent to tackle the dialogue scenes and retire to the trailer for the heavy stuff. Cavill is made of sterner stuff, and insisted on performing the vast majority of his own stunts. (He can’t share much details about the lone outlier, except to warn: “If you have two actors involved in that stunt, it increases the risk tenfold. And when we're talking about that kind of stunt, if the risk goes up just a little bit, people die.”)

Otherwise, what you see on screen is pure, unfiltered Cavill: from bathroom brawls to hanging off Pulpit Rock. “When you start doing the big stunts with the big boys, the adrenaline does definitely spike a little bit. The stuff off Pulpit Rock actually wasn't so bad, because it’s so high that you lose all concept of distance. It looks like a painting below you rather than a massive drop. It's only when you're closer to the ground that you fear hitting it.”

Spoken with a breeziness to make a million fans swoon.

If the Cruise Ankle was one big story from the Mission: Impossible shoot, the other was the Cavill Moustache. This magnificent specimen was inspired by a character from one of the actor’s favourite Superman comics, a villainous mercenary named Elias Orr. It also might have proved the most expensive moustache in history, at least for Warner Bros – during reshoots for Justice League, the studio had to spend a fortune digitally removing all traces of facial growth. (With mixed success.) Steve Austin was merely the Six Million Dollar Man; Henry Cavill has a multi-million pound upper lip.

While he admits, “had I known the Justice League reshoots were coming I'd have probably made a different choice”, the moustache also provided helpful camouflage. After shaving it, “I was in America for, I think, three hours, and I had been asked for eight photographs. When I sat down in a restaurant I was like, ‘wow, I forgot what it was like’.”

He makes a great Superman, and will doubtless make a great antagonist, in part because he engages with his characters; like the true fan, he understands them both within the logic of their universe, and their broader cultural heritage beyond it. In the past, Cavill has compared superheroes to the mythical Greek deities; what, then, does that make the modern action hero? The likes of Hunt, Jason Bourne, James Bond?

“The likes of Ethan Hunt and Bond are more our fantasy heroes,” comes the immediate response. “Because as much as they could be real people, it's just outside the realm of reality. It is reachable – but highly unlikely.

“You could see an Ethan Hunt type character suction cupping up past our window right now – but the chances of that happening? Extremely low – but it's possible. The chances of a guy in a blue suit and a cape suddenly zoom past at the speed of sound, or faster?”

He might be going downwards...

“Not at the speed of sound, though!”

Can’t really argue with that.

Growing pains

If Chris Hemsworth is the Aussie surfer ideal buffed to godlike proportions, and Channing Tatum the ultra-jock bestowed with charm and talent, then Cavill might well represent the English gentleman as we’d like to envisage him: impeccably mannered, sharp of wit and suit, possessing a vigorous dash of derring-do. The type of chap who carves out an eloquent 50* on a pristine village green, then leaps into a Spitfire still wearing his cricket whites.

His father served in the Royal Navy, and a brother is a major in the Royal marines. Although Cavill chose acting over the military, his diction – measured, precise – and his physique wouldn’t look out of place on the parade ground. Beneath the pleasantness, there is a glint of inner steel; put bluntly, Henry Cavill could kick the shit out of you.

But then being the fourth brother of five will teach a boy to toughen up. Born and raised on Jersey island, the Cavill childhood sounds rather idyllic, although he chuckles at my invocation of Enid Blyton (Famous Five and all that).

“I don’t know if it was Enid Blyton-esqe. I considered myself very, very fortunate. Absolutely.”

Apparently the fourth child has it cushy. “I could learn from all the mistakes of my older brothers, and also be protected by my mother if shit ever went wrong. Sometimes you step out of bounds and the older brothers will unleash fury and hell upon you.

"There was a huge amount of play fighting, and real fighting. Never punches in the face though. That was the one rule."

As well as the military, the Cavills have a solid Square Mile connection. After the Navy, Henry’s father became a stockbroker, and his mother worked as a secretary in bank – albeit only after the kids had grown up. “Her greatest job ever was being the mother of five boys, which is probably the hardest job known to humankind.”

Was Henry ever tempted to try the City?

Hollywood was a breeze in comparison to school. Rejection was just like, yeah, whatever.

“I don’t think a desk job is for me now that I’ve tasted otherwise,” says one of the biggest film stars on the planet. “I can see where the excitement lies in finance, I can see where the addiction comes from. My brothers are in finance. It can be enormously enjoyable. I could have gone into it, sure, and be working in a place like this on a daily basis, it would be awesome. But now I’ve experienced this idea of travelling for work, and I get to play a character, basically be a kid as an adult, it’s a tough one to replace.”

Cavill clearly dotes on his parents. Plenty of actors wax lyrical on parental support: “thank you, Mum, for telling me to always follow me dreams!” With Cavill, however, the gratitude stems less from their influence on his career than their moulding of him as a man.

“My parents are wonderful people, they’ve got a wonderful balance to them. My dad follows some rules very strictly and doesn’t follow other rules, and my mum has always been basically the perfect mother. Always caring, always providing us a set of guidelines, but also saying whatever we wanted to do was right and we would ultimately find our own path.

“My father set a wonderful bunch of guidelines as well, as far as just how to behave. The gentleman’s code. And what one must do in certain situations, and what one must do in other situations. And encouraged proper use of English language, and all these things. I really, really feel very fortunate that they worked so hard on us. If I ever have my own kids it’s something which I’m going to try and take lessons from and do my version of.”

What lessons would he impart to his children? What would be the Henry Cavill Gentleman’s Code?

“That depends on the world which they’re born into.” (As always, no hesitation.) “But ultimately the same sort of thing as my mother – which would be make the choices that you want to make, learn from them. These are the set of guidelines, this is what I consider good and morally right, and you can take that list if you want to, or not. Know that I’m here to help you: come and talk to me, ask me the questions, and know I’m going to be as fair as I possibly can.”

A solid set of guidelines...

“Yeah, right up until they become a teenager.”

I always look at kids who went to university and college with kind of a sense of envy

As a teenager Cavill was fat. How fat? Fat enough for his nickname at Stowe Boarding School to be Fat Cavill, “so I must have been a little bit overweight – at least compared to everyone else. I wasn’t obese by any means but I was fat. I was.”

I suspect many in his profession would try and bury such a nickname; Cavill shared it on Graham Norton. Along with self-deprecation, the willingness to self-critique is another tick on the list of Old School British Values that Cavill seems to embody; no melodrama, no gushing Instagram homily on the power of accepting the true you. He hesitates to label the nickname as bullying – “kids are flexing their social muscles at that age” – but his time at Stowe, during which he was often homesick, proved good preparation for Hollywood – a place not exactly renowned for its physical plurality.

“Hollywood was a breeze in comparison. Rejection was just like, yeah, whatever. I've been doing this for four years, alone, so I can definitely do it here. Especially when I'm getting paid.”

The 17-year-old who landed a breakthrough role in The Count of Monte Cristo is a handsome, almost angular young man acquitting himself well opposite Jim Caviezel and Guy Pearce. Yet when the adult version recently rewatched the film he was shocked by what he saw, or rather heard.

“I sounded like a Mickey Mouse version of myself! Didn't realise how high my voice was back then.” There is something quite comforting in the knowledge that even Superman winces at past incarnations. “It's amazing how much it's changed. I mean to be honest if I sounded like this when I was seventeen, it would be cool, but I was shocked. Really shocked. Very high. Like, very high.”

(I unearthed a few YouTube clips, expecting to hear the squeak of a mouse on helium. No luck: it’s not that high.)

Man of Steel

He made his name as Charles Brandon in the Tudors, and will surely be defined by Superman, but Monte Cristo is the film that changed Cavill’s life. “Suddenly I had a career. I was going to LA to try and find more work, meeting agents and going to studios to see if we could read scripts and stuff, and it became a job. So I got a job at seventeen which I'm still in now, and it became very serious and very real, very quickly.”

He gained a career but lost his adolescence, or at least some crucial part of it. “You stop being a kid almost immediately. You still do the normal stuff but you don't go to university and spend most of it drunk, and you don't go on your gap year and spend most of it drunk. You're running about the world, trying to make sense of things and make ends meet and all that. It's just a very different approach.

“I always look at kids who went to university and college with kind of a sense of envy because, as much as I'm really happy where I am, I also think it's just that thing: it's an establishment, it's a rite of passage, especially in England – you go to university and you do the university thing. Whether it's to play for teams, whether it's just going to lectures.

“I've never been to a lecture! I've never chosen whether I could go to a lecture or not because I had a hangover. It's a very weird thing, and I have no idea what that kind of studying is like. I would have loved to have done it, I would have done Egyptology or ancient history or something like that, but, yeah, I have no idea. And it's very bizarre for me because almost everyone else does.”

That “everyone else” says a lot. Cavill may have ascended into the celebrity stratosphere but he appears firmly grounded in what we might as well refer to as the ‘the real world’. (Not that private jets and film sets and five-star hotels are any less real than, say, Jersey or your commute to work.) A normal person might be the biggest oxymoron in the language but he is certainly a person you can relate to, despite the ludicrous unrelatability of his day-to-day existence. For someone who plays freaking Superman, this is perhaps the most impressive quality of all.

And as it’s not as though the role was bestowed upon him; to play Superman you must firstly believe yourself capable of playing Superman. Gaze into the mirror and see Superman gazing back. This “honest self-belief” is imperative: “if you don't have that walking into the thing, they can smell it a mile off, and they don't believe in you as someone who can be what Hollywood calls a star.”

He’s refreshingly clear-eyed on both the casting process – “a lot of getting a role is not down to one's acting, it's down to a look. If you can act, it helps” – and the subsequent effect of that casting, the transformation of personal life into public.

“I was always aware that things could change quite quickly. Once I got the Superman job, there was a turning point where I started getting stopped in the street in London, and people shouting "Superman!" They think that it's gonna make me turn around. You hear it, you think, don't turn around. Because then a whole street full of people go ‘what?’, and you're never gonna get where you want to go.”

He should look up and say, “where?”

“Yeah that's what I'm gonna do next time!” He chuckles. “That's a good one actually.”

Cavill loves Superman, and loves playing Superman. He is very good at playing Superman. It is his misfortune that his tenure has so far coincided with DC’s largely botched attempts to replicate the Marvel Cinematic Universe, with little of the preparation or planning. His debut, Man of Steel, remains the only ‘pure’ Superman film that Cavill has headlined – with Batman v Superman: Dawn of Justice and Justice League largely ensemble pieces more focused on setting up sequels than character or coherence.

Man Of Steel itself attracted controversy for its darker take on the Big Blue Boy Scout – Zac Snyder creating a moody film that felt closer in spirit to Christopher Nolan than Christopher Reeve. At the climax Superman snaps General Zod’s neck: a killing to save an endangered family, but a killing in cold blood nonetheless.

While fiercely proud of Man Of Steel, Cavill implies its story was intended to catalyse the more traditional, heroic version Superman for the direct sequels that remain unfilmed. “The killing of Zod would have led to a wonderful reason why Superman never kills. Not, he never kills just because his dad said so one day. He made the decision himself because of an impossible scenario, to which he then said, ‘I don't care if it's impossible again, I'm gonna find a way to make it possible in the impossible.’”

We wanted to create a company running on the lines of integrity and honour and fairness

The move toward a DC Universe meant “we didn't get the opportunity to show the other side of it, the ‘I'm ready to be Superman now and I'm ready to show the world the best examples’. That's where the joy and glee comes from, and that sense of warmth from the character, which is his real superpower – he makes people believe in themselves. It was a shame because it would've been nice, and it would have been a lovely coupling with the seriousness and the depth of Man of Steel.”

The real shame? While he does a fine, brooding Man of Steel, Cavill would be fantastic as the dashing Superman of our collective imagination. His featherlight turn as Napoleon Solo in the vastly underrated The Man from U.N.C.L.E. tends to be vaunted as a quasi-Bond audition, but Solo also proved Cavill a deft comic actor capable of blending silly and stoic.

He cites the complex, introspective Superman: For Tomorrow as “one of my favourite comic books. I would definitely like to tell a story like that”. Clearly he has unfinished business in the cape. “There's an opportunity to keep on telling Superman stories, and getting them exactly right. Showing the things like hope and joy and that wonderful power of his to make people believe in themselves.”

If Man of Steel 2 never materialises, perhaps Cavill can produce it himself. He recently co-founded his own production company, Prometheus Productions, with his brother Charlie and close friend Ben Blankenship as an antidote to the poison that has seeped through much of Hollywood. Having witnessed his fair share of “horror stories”, the ambition is for Prometheus to be run on the values of common decency as much as pursuit of cinematic greatness.

“We wanted to create a company which was obviously great at telling stories but was very much running on the lines of integrity and honour and fairness.”

Integrity, honour and fairness – that’s the Cavill Code for you. If we all tried to follow it, the world would be a brighter place.

Mission Impossible – Fallout is released 27 July