Colony In Space. Written by Malcolm Hulke, this is still quite a relevant tale of stripmining and greed and blind obedience.
this is the diffenrence between old and new Who really, the writers had their own bugbears (ecology, workers rights etc) and worked them into the scripts with a deft touch (mostly, The Sunmakers cough cough) whereas the new writers are merely hacks writing to a formula, though i shouldn't complain as no doubt this US redo will make them look like Joyce
AAAnyway.
Pertwee, Delgado (and Helen Worth!!) what's not to like??