The deafening sound of screaming girls greeted the arrival of Hollywood heartthrob Zac Efron for the UK premiere of his new film, 17 Again. The 21-year-old High School Musical and Hairspray star said: "It's insane. This is the biggest one yet. It's crazy." In the film, Efron plays the younger self of Mike O'Donnell, a frustrated and unfulfilled 37-year-old, played by Friends star Matthew Perry. The character seemingly has it all as a star athlete heading straight for a college scholarship until he decides to give it up and settle down with his high school sweetheart. But at 37, Mike has become a miserable and unhappy businessman who wishes he could go back and become the teenager he once was and to correct all the mistakes he made. His wish soon becomes reality as he turns 17 again and gets the chance to relive his life. With a cavalcade of fans chanting his name in in London's Leicester Square, Efron said: "I can't wait to see what everybody thinks, this is a movie to bring along the fans, I want to bring them along to a new adventure." Asked if he would be prepared to do a full frontal nude scene, said: "You look so excited. I don't know. Honestly, I don't know."