JAMES McAvoy and Michael Fassbender have taken on a daunting challenge in stepping into the shoes of Professor Xavier and Magneto.

But the rising young stars recognise there’s as much pressure in reprising roles best known for being played by Sir Patrick Stewart and Sir Ian McKellen in the X-Men series. So the choices before them were clear when they were signed on to appear as these characters in the big budget prequel X-Men: First Class.

“The comic book history is different from the X-Men movies that have come out before,” explains Scotsman McAvoy.

“In the comic books my character is American, but when they made the original films they decided to make the character English.

“I watched the other films, but with the knowledge that this was a prequel so it had to be fresh and offer something new. So I looked at Sir Patrick’s performance and took a lot of notes on it, but it was more about seeing how I could make him different.

“Where Sir Patrick was wise I would be foolhardy; where he was chaste I’d be randy, you know what I mean? Then if we make any money and make three films, I’ll end up doing something more like Sir Patrick Stewart, but initially it was really important to start from a different place while taking the cues from his performance.”

While the first X-Men film released 11 years ago introduced Xavier and Magneto as enemies, this drama shows their early friendship as they struggle to come to terms with their mutant powers in a story that cleverly weaves its way through 20th century history.

Fassbender concentrated less on McKellen’s interpretation of his character than the Marvel source material.

“I just used the comic book,” he says, “and I was spoilt because there is so much in the character’s biography that I could to draw from.”

Director Matthew Vaughn has delivered a hugely enjoyable origin story that plays to fans of the series and newcomers alike. The plan is clearly for a trilogy of prequels to bring this strand of the story together with the beginnings of the first X-Men movie that was released into cinemas.

And for that, McAvoy realises, he might have to emulate Patrick Stewart even more literally and sacrifice his hair in order for Professor Xavier to seamlessly become the man audiences first met.

“In the comic books he loses his hair the day that his powers activate within him when he’s very young,” adds the actor. “But we decided not to do that here.

“Maybe it’s a smart move in an origin story.

“We’ll see why he loses his hair in another movie. I don’t know how we’ll do it, but I’m sure we’ll come up with something cool.”