Last of the Time Lords
The "Doctor Who" episode "Bad Wolf" (2005) mentions a futuristic version of "Countdown", in which the goal is to stop a bomb from exploding in 30 seconds. "Countdown" was referenced again in a later series in "Last of the Time Lords" (2007), where Professor Docherty expresses a keen fondness for the show and how it "hasn't been the same since Des took over—both Deses".