Jon Pertwee as The Doctor

Katy Manning as Jo Grant

Nicholas Courtney as Brigadier Lethbridge-Stewart

John Levene as Sergeant Benton

Richard Franklin as Captain Mike Yates

Stewart Bevan as Cliff Jones

Jerome Willis as Stevens

Tony Adams as Elgin

Ben Howard as Hinks

Mostyn Evans as Dai Evans

Talfryn Thomas as Dave

Roy Evans as Bert

Mitzi McKenzie as Nancy

Ray Handy as Milkman

John Scott Martin as Hughes

John Rolfe as Fell

John Dearth as BOSS (voice)

Richard Beale as Minister of Ecology

Jean Burgess as Cleaner

Brian Justice as Yates' Guard

Terry Walsh as Guard

Roy Skelton as James