Ed Helms admits he was terrified to read the script for the new Vacation movie. "I just thought, 'No way, this is sacred!' This is one of my favourite movies," he says. "I think it was my manager who just said, 'Don't be an idiot. At least read it.' And as soon as I read it I realised it wasn't a remake. It was technically a sequel, just 30 years later."

Ed Helms with Vacation originals Chevy Chase & Beverly D'AngeloEd Helms with Vacation originals Chevy Chase & Beverly D'Angelo

The 1983 original spawned three sequels (in 1985, 1989 and 1997), and this summer's movie picks up the story with the next generation, with Helms playing the Griswolds' son Rusty. "This film is all new," he says. "So I can look at this character and really just bring my own instincts and energy to it. That felt great."

This also means that the movie has a different tone. In the original Vacation, he says, "there's very little narrative character development, and the characters have virtually no consequences for their actions throughout the whole movie, which is part of the delight of that movie. But I think that's a hard sell in 2015."

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Helms' favourite part of filming this was when Chevy Chase and Beverly D'Angelo were on set for three days reprising their roles as Rusty's parents. "To have them in the movie and even just to have them on set was the ultimate affirmation for all of us," Helms says. "They showed up with great positive collaborative energy. They were like royalty, and they couldn't have been more psyched and fun and playful."

Shooting the movie around Atlanta also brought back some personal memories. "I'm the youngest of three kids, and we took lots of road trips from Atlanta when I was a kid," he says. "It was a four or five-hour drive to the beach. We did it all the time, and back then air conditioning in cars wasn't so good. We'd get in the car, excited to go to the beach, then everyone gets overheated and angry, and you get out just angry. But then of course being at the beach makes it all good."

Watch the trailer for Vacation here: