IT was on one of his first days on the set of X-Men: First Class that the true scale of his latest job hit James McAvoy right between the eyes.

"With the Atlantic ocean stretched in front of us and helicopters flying here, there and everywhere, it was pretty epic," McAvoy recalls.

"(Co-star Michael) Fassbender and I had to stand on the beach, facing out to sea, with no crew around us - there were a few more actors, but like miles behind us - so we felt completely on our own.

"A helicopter started a mile out at sea and it flew at us really low to do like a pass-over shot. It was totally an optical illusion 'cos it must have been 50 feet above our heads, but as it was getting closer and closer and closer, the blades looked completely in line with our faces and both him and I were laughing, giggling with fear.

"At that moment you went, 'F--- me, this is a big old massive piece of good movie nonsense'."

If anyone was going to find the going on a massive blockbuster like X-Men: First Class nonsensical, it was McAvoy.

Though the 32-year-old Scottish actor has had his comedic moments (cult TV series Shameless) and his action blowouts (Wanted), he's really made his reputation through serious dramatic fare - The Last King Of Scotland, The Last Station, Atonement and mini-series State Of Play.

And McAvoy has made no secret of his disdain for the Hollywood machine. So how did he come to play the leader of the X-Men, Professor Charles Xavier, in the reboot of one of the biggest comic-book movie franchises of all?

"I know what you mean, it is kind of a strange one," says McAvoy, laughing the laugh of a man who's just been caught out.

"But you know what? I felt like I needed to work with somebody who was fun like (director) Matthew Vaughn, and work on a script which, for my money, is more fun than the previous X-Men movies in terms of its levity and humour.

"Also, I was a fan of X-Men from the cartoon when I was a teenager. So it was too attractive a prospect to turn down.

"And, we filmed it half an hour from my front door, which never happens as an actor. It'd be good if that became the headline of any interview I do - 'It was simply through vicinity that I decided to do this film'."

Yes, staying close to London loomed large in McAvoy's calculations on First Class - he and his wife, actor Anne-Marie Duff, welcomed their first child, son Brendan, last year. Working so close to home, he says, "you get to see your family and friends and you get to not have jetlag every time you go to work".

There was also the "shake it up" factor.

"The films I'd done before it, they were smaller films, more character-driven pieces," McAvoy says. "As ever, I want to try and shake things up - not for an audience, not for anybody else, just for me."

But it also becomes clear that McAvoy simply knew he'd have a ball making the blockbuster. And he did. So much so, he's already talking about doing a second and third Class.

"This is definitely true - I have had enough fun to expect to go on and do more. However, I am also legally obliged to go on and do more if they so choose to make more," he laughs. "So either way, I'm sure I'll be there - unless they decide to fire me."

The fun McAvoy speaks of is all over X-Men: First Class, which takes the story back to the days when Xavier and Erik "Magneto" Lehnsherr (Fassbender) first met - in the swinging '60s.

Lehnsherr is a man traumatised and set on revenge, but the young Xavier is enjoying his mind-reading powers to the hilt.

McAvoy insisted on some script tinkering, adamant that his Xavier must be a much looser character than the wise old (and bald) Professor played by Patrick Stewart in the previous X-Men films.

"The first scene was always written with him chatting up a young student," McAvoy explains. "When I first met Matthew I said, 'Listen, can we really take that and run with it, can we make him a rubbish flirt?' He's gotta become the wise, sage leader of this band and all that, yes, of course, but if you don't give him something else he might as well just be played by Patrick Stewart."

(For the record, McAvoy swears those scenes where Xavier is a "rubbish flirt" didn't require too much acting. "I am an absolutely rubbish, rubbish, rubbish flirt. But I enjoy playing people who think they're good at flirting but they're not," he laughs.)

Xavier and Lehnsherr gather the first team of mutants, joining forces with the CIA to fight a mutant baddie with the Russians on side. By close of play, Xavier and Lehnsherr's friendship is fractured, setting them on course to becoming the arch-rivals played by Stewart and Ian McKellen in the previous films.

McAvoy and Irishman Fassbender (Inglourious Basterds, Hunger) have known each other since working on Band Of Brothers in 2000, so their First Class double act sprang to life quickly.

"When we met up to talk about doing this, we both agreed there's no point in making these big, silly pieces of fun unless you can enjoy it, too," McAvoy says.

"As hard as it was at times - because these things are very hard to make, they are a storm happening all around you every day for six months - we made a pact to try to make each other laugh as much as possible."

In a fab montage, the pair go on a recruiting drive, in which they perch on a strip-club bed.

"That scene got exceptionally silly at one point," says McAvoy. "I don't know if I'm even allowed to tell you what originally happened. But it got pretty f---in' kinky. I'm not joking."

Was the dashing duo's bromance, uh, consummated?

"Unfortunately no. But there was a little bit of cross-dressing going on. That's all you need to know."

(For the record, McAvoy would have preferred it if Xavier and Magneto stayed together. Like, really together. "It is a little bit of a mini-tragedy that him and Magneto don't, you know, have sex and become married and become best friends.")

Though still young, McAvoy seems an incredibly well-travelled actor. His policy of mixing it up will continue with the animated Arthur Christmas out in November and a London crime thriller, Welcome To The Punch, to shoot soon.

He doesn't scoff at the term "veteran".

"I mean, I have been doing it a long time. When I did (British comedy) Starter For 10, I was 25, and even in that I was the only one with a lot of experience," he laughs.

"On X-Men, Fassbender and I often felt like granddad. Fun, cool, likes-to-do-stuff granddad. But sometimes you'd be left totally outside of the reference of a conversation. Rose Byrne and I a couple of times caught each other's eye and gave it a, 'F---in' hell, what are we doing, man?' But that's the joy of getting older - you know your place."

McAvoy also knows there is a place for mind-reading. And that place is only in the movies. He did not bother to attempt any of Professor Xavier's mind-control tricks off-set.

"If I was that method actor, I would gladly ask somebody to shoot me," he groans. "It's just my ego that makes me think I know what anybody's thinking."

* X-Men: First Class opens today

Originally published as James McAvoy is a classy man