And they really are famous, you know. Over 4,500,000 people subscribe to their channel. It's a surreal thing to happen to two very normal guys from a small Oxfordshire town, Thame, who one day decided to film some silly stuff in slow motion and upload it to the internet.

When I met them at YouTube's offices in London, they certainly didn't act like celebrities, and seemed to find the whole thing almost as surprising as anyone else.

"I was at the airport today," Gruchy said. "I was at the x-ray machines and the guy told me to take my belt off. And of course, as I'm going through he says, 'Stop sir, you'll need to do that in slow motion.'"

Everyone loves them. "We get stopped a lot in Thame," Gruchy said. "You get a lot of older people saying, 'My son loves you, he'll be so jealous I've met you.'" Free said his dad recently had the police round after he'd been robbed, and the officers were stunned to see his picture sitting on the mantelpiece.

YouTube is currently running a huge poster campaign featuring the pair, which they find simultaneously awesome and – being British – deeply embarrassing. "It's so surreal at the moment," said Free. "I'm only back for a few days [he lives in Texas], so we went down to the underground to look at the giant poster of us. We knew what to expect because someone had tweeted us, but when I saw it in person, I was like, 'Oh, god' – I wanted to hide."