The 19-year-old Nowhere Boy star - who is engaged to Sam Taylor Wood - plays a normal high school kid who decides to re-style himself as an amateur superhero, complete with green wetsuit, in Matthew Vaughn's action comedy.

Aaron revealed: "It gets pretty sweaty at times if you're fighting constantly and I had to wear a jockstrap, so it was uncomfortable, but you get used to it."

He added: "I was in the costume probably every day for about 12 and a half hours a day, for three months. Only two toilet breaks a day. It was enjoyable, but it was mad."

The young actor, who has won critical acclaim for his performances in Kick Ass and Nowhere Boy, previously had only minor roles to his name and was delighted when he landed the title role after fooling director Vaughn with his American accent.

He revealed: "I was used to reading tons of scripts out there at the time and usually really crummy high school movies, you know, boy's a badass guy who loses everything and he gets the girl, they were really rubbish, typically cliched, unoriginal scripts and then this came along. It was kind of Superbad meets Kill Bill, it has this mad edge to it, it was a dark comedy."

:: Kick Ass opens in cinemas on Wednesday March 31.