The answers to my Star Wars/Doctor Who puzzler then.

Nick correctly identified Leslie Schofield (Caleb in The Face of Evil and Leroy in The War Games), Don Henderson (Gavrok in Delta and the Bannermen), Dave Prowse (the Minotaur in The Time Monster) in the Vader costume, and Peter Cushing, who played Dr. Who in the two 1960s Dalek films.

The other Who actor in the scene – which I only discovered while checking my facts before putting this up – is Cy Town, who plays one of the guards (“Imperial Trooper Guard Tajis Durmin”, apparently) and has an absolutely massive list of Doctor Who credits, albeit many of them uncredited. He was a Dalek operator in every Dalek story from Frontier in Space to Remembrance of the Daleks, and was also in Spearhead from Space, The Silurians, Inferno, The Three Doctors, Invasion of the Dinosaurs, The Android Invasion, Revenge of the Cybermen, The Masque of Mandragora, The Invisible Enemy, The Sun Makers, Castrovalva, Enlightenment, Attack of the Cybermen, The Happiness Patrol, and The Curse of Fenric. And he gets extra points for playing, uncredited, a technician in the last episode of Blake’s 7.