Speaking on ITV1's Daybreak, the actors also spoke about the universal appeal that they believe the show has.
When asked by host Adrian Chiles where they felt the series could progress next following its gradual transition from BBC Three to BBC One, Barrowman and Myles replied in unison: "Movies!"
"They don't know about that yet," Miles added.
Barrowman then quipped: "We're writing it, it's just all about us isn't it?"
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When asked why Torchwood is so popular, Barrowman explained: "I think it's because [audiences] can relate to the characters. Although we're sci-fi and we have a heightened reality and we do very 'bigger than life' things, the relationships between the characters and the personalities - if I can toot our own horns a little bit - we bring a little bit to it... People can relate to it, and I think that's important.
"We represent everybody out there. If you watch it, you can find some of yourself in one of the characters."
Myles added: "Yeah, as John says, there's huge sci-fi elements in it, but there's an awful lot of domestic drama in as well.
"There's [also] great humour in it - for all the dark moments, you've got something humorous to kind of lighten it."
Torchwood: Miracle Day continues on Fridays at 9/8c on Starz in the US and on Thursdays at 9pm on BBC One in the UK.
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Watch series creator Russell T Davies discuss Torchwood: Miracle Day with Digital Spy below: