YouTube stars Zac Alsop and Jamie Rawsthorne have a history of mischief on their channel, which has close to 400,000 subscribers. In Pants On Fire, they'll be claiming they snuck past security into a world class athletics event to sprint the 100m, got hands on with Leonardo DiCaprio and became Death Diving champions in Norway - but how much is truth and how much is lies?

How did you first meet?

Zac: We met at university. We did a degree in Team Entrepreneurship, which is basically like The Apprentice. We were the first ever UK course to do, but it was a bit weird because there were no lectures and no exams, so we were just put into groups and told to run a business. That's where me and Jay first met. We went on a night out in freshers week and he cooked me a bacon tortilla wrap when we got home, so I knew he was a stand-up guy.

Describe your partnership.

Zac: We run a YouTube channel that's essentially showing people that we're living in the best time to be alive in the world right now. You can create anything, connect with anyone and be whoever you want to be. We don't think there's any other time in history when people have been able to do that for a living. We're two everymen on a mission to enjoy life.

Jay: We're willing to push boundaries and do things a bit out of the ordinary.

How did you start doing YouTube videos?

Zac: I started just out of university. I was always into YouTube, and I started doing videos on the sort of things me and Jay were doing anyway like sneaking into festivals, because we were broke students with no money, and just documented that process. It was my personal channel but Jamie was part of the videos from the start, and two years later Jamie decided to park his business and go on this mission together.

When was the moment you realised you'd become popular on YouTube?

Zac: We always knew that the stuff we were doing had the potential to be shocking enough or crazy enough to be popular on YouTube. The first video we uploaded was a stunt where we dressed up as Olympians and jumped on the homecoming parade bus and everyone thought we were gold medallists. We went around the whole day getting free drinks and letting people hold the fake medals we bought on eBay. We ended up partying with all the Olympians and Will.I.Am. That got national press overnight before we had even got home from the night out.

What was Will.I.Am's reaction?

Jay: He was on a table in a little private section near us and he said "Oh my god, you guys are like Zorro" because we told him we got gold medals in fencing. We had a good little conversation with him about fencing and the Olympics in Rio when we were just lying through our teeth the whole time.

This is you first TV series - how does it differ from making videos for YouTube?

Zac: We get dusted up with make-up everytime we're on camera which is quite nice. To be honest, it's a whole operation. To do the stuff we go out and do on YouTube as just the two of us, there's a whole lot less moving parts, whereas this is a whole operation. It's all handled for you, so we don't have to worry about every aspect. You've got directors and cameramen to do things. It's nice being able to enjoy the moment a bit more with each experience rather than worrying about the operational side of things.

Is it true you've pranked a TV show before?

Zac: Yeah, we did. The One Show had Louis Theroux on and they were interviewing him about his new documentary series. One of our friends runs nightclub events to do with Louis Theroux - sort of Louis Theroux appreciation nights - and they got a message from a researcher at The One Show, but they didn't want to do it. So we set up a fake email and intercepted that opportunity, convinced them that we were the ones who operated those club nights and then 10 hours were live in the studio on national TV with Louis Theroux, wearing Louis Theroux t-shirts, pretending we run a Louis Theroux club night. We went down on our hands and knees and bowed to him on national TV which was really funny.

Are you actually fans of Louis Theroux?

Zac: I think he is a national hero, so although we were doing it in jest and we weren't the ones running the Louis Theroux organisation, we did actually mean it from a heartfelt place.

You are the 'professionals' on the show and your back catalogue includes a lot A list stars - tell us about those?

Zac: Will.I.Am and Team GB were in the very first video we recorded. I made it into the ring with Anthony Joshua in one video. I was in Connor McGregor's dressing room when he cut his 30th birthday with just him and a team of his closest friends. Jamie got in front of the world's press right next to Brian May and a load of other celebs at the BAFTAS. We infiltrated the red carpet, and the Royals were there that night.

In Pants On Fire, is there a rivalry between you and the other competitors?

Zac: I think naturally, yeah. The first time we met them we were facing off in a boxing-style standoff. I think that set the tone for the rest of the filming. We were quite secretive over the challenges that we were doing, and they were secretive about theirs.

Jay: It was friendly banter really. We got on really well with them by the end of it.

Who was the best detective?

Zac: Jimmy Carr. His bullshit detector is quite good. As soon as the cameras were on he went straight for the jugular. He mugged us all off pretty much in the first minute of recording. He was even trying to pry at us in make-up before the cameras were on.

These challenges really get the adrenaline going. Which challenge were you most nervous about attempting?

Jay: Death Diving for me. It was 11 metres and we'd heard of people who had fractured their faces in three places.

Zac: I've never felt so unqualified for anything in my life. In terms of thrill, I really enjoyed the red carpet one. Me and Jay were hiding out in a toilet for four hours and the pressure was getting higher and higher until we knew that Leonardo DiCaprio and Brad Pitt were arriving.

What challenge that another team did would you have loved to have tried?

Zac: We really wanted to do Wimbledon. We had an idea around Wimbledon that was different to Donna and Verona's, but you can't have two teams going at the same prize.

Were there any challenges that you absolutely would not want to do?

Zac: Bobby went on Babestation. I've never seen anything so embarrassing in all my life! The outfit he had to wear! I don't think I could have mustered that one. And the Mexican wrestling looked quite horrible. I've got a slipped disc in my back, so I don't think it would have been favourable for me anyway.

Emma was playing along too. How good was she at spotting when you were lying?

Zac: I think by the end of the series, she was more confused than ever! There were parts where off camera she would say "I can't believe you even attempted this". I think she got less and less trusting of the things we were attempting and the things we were achieving. We probably confused her more than anything else.

Do you tell lies in your real life?

Zac: I like to think we're quite authentic trusting guys in everyday situations, but our everyday requires us to lie quite a lot because of the things we do on a weekly basis for YouTube. So by virtue of that, we do have to lie quite often.

Have you ever told a lie that got out of hand?

Zac: That we know what we're doing! Every time we do these things we're quite surprised by what we achieve. And now we've been dubbed "the professionals" on a national TV series. I feel like we've been blagging the world at pretending we can blag! We started the ball rolling and had to keep up with bigger and bigger ideas and every single time we think the odds are against us we somehow manage to pass. So doing the YouTube stunts and now this show is sort of like a lie that got out of hand for us.

What's a true story about you that sounds like an outrageous lie?

Jay: I used to run a tech company involved giving people analytics and hired a team of PhD data scientists to sell software to unis. And now I'm sneaking into places on E4.

Zac: Me and my mate bought Olympic outfits that were reduced at JD Sports, got drunk at 11am, and managed to get on the Olympics homecoming parade with the world's best sportspeople. And Will.I.Am.