YOU join us in that cradle of civilisation, Greece. But there won't be much sun protection required on the Adriatic this afternoon: the skies are thick with murderous thunder and lightning.

Despite the inclement weather, a bunch of manly men - 300 to be precise - are standing around in little more than leather loincloths and comfy sandals. They are shouting "hoo-hah!" and beating their chests as their mulleted hair flaps in the wind. They have an urgent appointment at the Hot Gates. No wonder they're eagerly stroking their swords.
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No, they're not German tourists, and nor is the Hot Gates a lap-dancing club. They're elite Spartan soldiers, the toughest of the tough in the warrior culture that defined the Ancient Greek city state of Sparta. Back then, no one messed with the Spartans; hundreds of years of battlefield dominance had seen to that. But now, with the time fast approaching 480 BC, Sparta is under attack from the evil god-king Xerxes. He wants to conquer Sparta like he's conquered much of the rest of the known world. But he knows the Spartans are macho guys. So just to be sure of victory, Xerxes sends a big army to fight them. A really big army. A million-strong army, in fact, with lump-faced giants, phantom soldiers with sharpened teeth, armoured elephants and battle rhinos thrown in for good measure.

"Come and have a go if you think you're hard enough" - or ancient Greek words to that effect - says Sparta's King Leonidas. He positions his 300 soldiers at the Hot Gates, a narrow corridor between cliffs through which the Persians will have to pass. Let the Battle of Thermopylae - one of the greatest ever, military history fans - commence... But hang on - is King Leonidas speaking with a Scottish accent? Indeed he is. That's Gerard Butler playing the lead the role in 300, a full-on period film based on the graphic novel of the same name by Frank Miller (Sin City, The Dark Knight Returns).

In this epic the 37-year-old from Paisley is rippling with so much muscle as to be almost unrecognisable. He has played more than his fair share of action/hero/macho roles, from Beowulf to Attila The Hun, to Lara Croft's boyfriend in Tomb-Raider to The Phantom Of The Opera. But in this big-budget blockbuster he takes the energy biscuit.

"It wasn't about becoming Schwarzenegger," Butler says of his bulging bod. "I wanted to have power and agility and speed - but I also needed to bulk up to fill the role of the king. I had the armour on my arms designed in a particular way so you could literally see the veins and the meat bulging out of the side. My arms were massive! I'd be working on them with weights and I'd feel my arms were gonna fall off. But I just didn't stop."

For seven months, Butler and his fellow cast members, with the aid of a team of trainers, went overboard in the gym. He adhered to a strict protein-rich diet, and for the duration of the shoot he even gave up the full-strength Marlboro Reds which, during our lunchtime rendezvous in Los Angeles, Butler smokes like there's no tomorrow. Just as you've never seen Butler like this, you've never seen a swords'n'sandals epic like 300. It uses cutting-edge digital technology to create an ancient world with an almost painterly quality. Against this, director Zack Snyder (Dawn Of The Dead) and his team of stunt coordinators set up a beautifully orchestrated orgy of spearing, chopping and beheading. "It's a warrior ballet," says Butler.

"You knew you were climbing into a different world. There was something very un-Hollywood about it. It didn't feel like a stoodio film," he adds with a hint of an American twang. "Even though it felt like a big film, the characters weren't your typical epic-style characters. I often felt we were more like the bad guys. You know, this is no Troy, this is no Alexander - I didn't have time for either of those movies. They were flogging a dead horse there."

This sunny lunchtime in LA, Butler is less like a king than a laidback dude in artfully distressed jeans, leather jacket and an array of bangles and threads adorning his wrist. He has apartments in London and New York these days. But, having lived in LA on and off for a couple of years, he's West Coast in both senses: bit of a Glaswegian wide boy, bit of a Hollywood player, with the occasional lapses into California spiritual speak and American accent to prove it. He also brings with him the tiny wee dog - a miniature pug named Lolita - that, in some La La Land circles, speaks of celebrity status.

He looks his 37 years, with crinkles round his eyes and grey in his hair. But he's still buff some months after finishing filming 300, a legacy of the intense makeover to which he subjected himself for a film that may - after years of 'next-big-thing promise' - finally propel Butler into the spotlight. His fitness today is also the legacy of a more humdrum obligation for the rising Hollywood star: he's just been photographed for the cover of Men's Health, and had to rediscover some of his 300-era shape. "And I just didn't have the same motivation," he grins. "I was also about to shoot a love scene with Hilary Swank."

Butler has been filming in Ireland with the double Oscar-winning actress in a romantic comedy called PS I Love You. "The truth of my character was that he was a limo driver who liked beer."

Butler had to convincingly show off his pecs for the benefit of the magazine... and then his beer belly for the movie. "I went from one body to another in nine days!" Such intensity - of work, of obligation - suits Butler. He came to acting relatively late, after abandoning his legal career in Edinburgh just before he was due to qualify as a solicitor. He enjoyed a roaring twenties, drinking too much and doing "stupid" stuff like hanging off buildings and dodging traffic.

"One of the things we would do as lawyers at the fancy dress Halloween cheese'n'wine ceilidh is drink a glass of wine and smash it off our heads. I always had to go that bit further. I would line up five glasses then smash them off my head. One night I did it when I was in Paisley with my buddies. I was so drunk I stuck it right in my nose! It bled for six hours; I lost so much blood I was getting weak. And I had this big flap of skin hanging off."

He can laugh about it now, with the easy confidence of someone who hasn't touched a drop for "nine years and one month". No, he'll never drink again, and, no he doesn't miss it. "I'm at the stage where I've never had a drink. I have no connection to it whatsoever. The smoking is my next battle. But we're born on earth to be set with these challenges."

But he doesn't want to get "too deep" into the self-destructive aspect of his nature back then; it's too pat, he says, to draw a link between his father being absent for most of his childhood (they were reconciled, but he died of cancer when Butler was 22). "They were crazy times," he admits. "Some of them were done in fun. Some of them were done through a lot of pain that was going on. But now I love the fact that all of that's happened. It's toughened me in a severe way."

Still, his walks on the wild side may come in handy for his lead role in his "passion project", a biopic of Robbie Burns. The as yet unmade production is long running and oft discussed, and it seems Butler has been annoyed by snarky comments on who might appear in the movie with him.

"This is where I wish people in Scotland would understand. People speak out when they really have no idea about the economics of putting a movie together - perhaps when we make it there'll be a couple of Americans in it. And they'll get pissed off about that. But if there weren't it might not have been able to get made. You're trying to make what is an incredible story about an incredible man. But it's period, which is expensive and risky, because much as we love Robbie Burns, trust me, he's not as known around the world as we think he is. Especially not in Los Angeles!"

Still, he's confident they can finally start filming next year. "And hopefully if things keep going the way they've been going for me then it'll be far easier to make the film."

Indeed. Butler is by no means a household name, but he has achieved a rewarding twin-track career (with the 'bi-coastal' lifestyle to match): roles in big Hollywood-friendly fare alongside performances in more thoughtful material including Dear Frankie. But if the advance buzz on 300 is correct - Butler says that in test screenings it scored better results than any previous movie made by Warner Bros, including The Matrix - he may, finally-at-last-no-really, be about to break into the big time.

300 may be a bit daft and OTT; all the hacking and chopping does get a little tiring after a while. But it's truly an eye-frying feast. And it may well have paunchy British men scurrying off to pump some iron sharpish.

"If it does, that can't be a bad thing," laughs Butler, as he draws enthusiastically on another fag. "I hope it doesn't send them home to spear their wives."