Noel Clarke's character Gordon saying he's in post-production for Doctor Who (as a director) is a joke, playing on the fact Clarke was one of the stars of Who.
Zoë Wanamaker, Fenella Woolgar, Steve Pemberton and Noel Clarke have all appeared on Doctor Who, 9th and 10th Doctor episodes.
Reece Shearsmith has also appeared in Doctor Who, with the 12th Doctor.