Doctor Who: You will believe

Peter O'Brien as Ed Gold in Doctor Who: The Waters of Mars.

Peter O'Brien says the British sci-fi works so well because the audience suspends disbelief.

When he stepped onto the set of Doctor Who in Cardiff earlier this year, Peter O'Brien knew he was in for something different.

In "The Waters of Mars", the Australian actor plays Ed Gold, the second in command at Bowie Base on Planet Mars.

"It was fantastic. You are transported into that world the moment you step into it," he says. "It's an odd thing to say but it's more than just an acting job, because you're in that Who world. It's the dialogue, and the way it slips into our world is so different to everything, and you approach it in a different way.

"There were never any moments of self-consciousness from anyone. If there's an acting style that comes with it then it's slightly different to just doing any other sci-fi drama. There's a heightened reality to it which is terrific."

O'Brien, who recently appeared in Underbelly, landed the role having previously worked for executive producer Russell T. Davies on his earlier series, Queer as Folk.

The popularity of Who is so ferocious in the UK , he was sworn to secrecy on the finer detail of the special, one of the last to feature David Tennant.

"He's such an iconic Doctor. But that's why it works, people believe it. They allow themselves to be transported into that world. Now sure, that's happened because it's been there for years but people had to make that leap of faith early and I think it was always above everything that was being done.

"But to do that you have to spend money on production. The moment anything starts to look fabricated your audience starts to doubt it. That's one of the things about Doctor Who, even though the Daleks originally once looked dodgy," he said.

"It takes you beyond what your normal television viewing is."

Doctor Who: The Waters of Mars airs in Australia at 7:30pm Sunday on ABC1.