BRIGADIER: The man was mad.

DOCTOR: Yes, well, of course he was mad. But at least he realised the dangers this planet of yours is in, Brigadier. The danger of it becoming one vast garbage dump inhabited only by rats.

BRIGADIER: It’ll never happen, Doctor.

DOCTOR: It’s not the oil and the filth and the poisonous chemicals that are the real cause of pollution, Brigadier. It’s simply greed.