The Doctor's assistant Bradley is played by one of the writers; David Clarke. As with Tony Garner he's a keen amateur actor, having been in many local productions in the Hove area over the years. So far the later part of the story has not been filmed, where his character "Bradley" is revealed to be none other then "Auriga", a renegade timelord engineer who has his own designs on the cosmos. This later change presents the biggest challenge for David - the need to show Auriga as evil but without the cliche moustache-twirling or the "dress-for-the-occasion" of the Eric Roberts's Master in 1996's Dr Who film.
Here he is with the Doctor, exploring the dome
and here negotiating with the daleks...
and here in his character's Tardis - filmed January 2005