I fully expect to be told in 2015 that, despite having nothing nearby
that could conceivably be impacted by the discharge from my (modern)
septic tank, I will have to fork out serious money for a fully
functioning mini treatment works costing tens of thousands of pounds
to cope with the excretions of one human being.

A fully installed mini treatment plant that will serve a household of six
people is around £7,000 not the ridiculous figure you suggest.