James is playing Britain's Got Talent winner Paul Potts in a biopic depicting the phone salesman-turned-opera singer's life.
He was spotted on set with Mackenzie Crook, who also stars in the movie with Julie Walters, Jessie J and Colm Mean.
Britain's Got Talent head honcho Simon Cowell is even rumoured to be making an appearance as himself in the movie, titled One Chance.
Director David Frankel – also responsible for The Devil Wears Prada - previously told Digital Spy that if the film were to feature a recreation of Paul's audition, the music mogul would appear.
"I haven't met him or talked to him, but one of our producers is in touch with him a lot. He's been very supportive from afar," he said.
"He loves the story – it's just a testament to the power of his shows."
James has already been spotted filming scenes in Venice, Italy, where he was kissing actress Valeria Bilello.
One Chance follows Paul as he overcomes the obstacles to get his singing career off the ground, before entering the 2007 series of the ITV1 talent competition, which he won.
James is no stranger to the big screen, following his roles in The Three Musketeers, The History Boys and Gulliver's Travels.