David Walliams will play a cowardly mole-like alien in 'Doctor Who'.

The 'Little Britain' star will have to spend hours in make-up for the role in the BBC sci-fi series in an episode which has been written by 'Being Human' creator Toby Whitehouse.

A show insider said: "They thought he would be perfect for the role of alien Gibbis. He is well known for his love of prosthetics on his comedy shows so this won't be much different to him."

The episode is due to air in the second half of the next series - which is being split into two separate runs, with the first episodes airing from April and the next shows rumoured to be starting in September.

David revealed he had landed a part in the programme earlier this month and admitted he was thrilled to be joining Matt Smith - who portrays The Doctor - because he is such a huge fan of the series.

He said: "I've actually been offered a part in 'Doctor Who', which I'm very, very excited about. I've said yes. I don't think I can say much, but I'll say I'm an alien."

David's casting details are the latest development on the new series to have been revealed, other secrets include a pirate-themed episode, the return of River Song and a storyline which takes place in America at the infamous Area 51 site - which is allegedly used by the US government to study aliens.

Despite the BBC's best efforts to keep everything under wraps, actor Nicholas Briggs - who voices the Daleks, Cybermen and Judoon monsters in the BBC sci-fi series - insists their efforts ultimately prove to be futile.

He told BANG Showbiz: "When you get your script your name is watermarked all the way through it so if you give it to someone else it's traceable back to you. Every time I've done 'Doctor Who' I always find it hilarious that by the time I get there and do the filming when we come back everything we've been doing is already on the internet.

"It's very laudable that the BBC keep it all secret, but it's kind of futile really. But its part of the fun, it creates more of a buzz about the show."

Nicholas has been busy recording vocal parts for the 'Doctor Who Experience', which opens this Sunday (20.02.11), and features an interactive 3-D adventure with The Doctor in the TARDIS and an exhibition featuring props and costumes from the show's entire history.

Among the items on display are Daleks, several generations of Cybermen, Davros - the Daleks' creator - robot dog K9, a Zygon and TARDIS control rooms from different eras.