score:2
Japan does not require the six months.
Any foreign visitor who wishes to enter Japan must have a passport, which will remain valid during the period of stay.
from http://www.jnto.go.jp/eng/arrange/essential/visa.html . There are numerous less-official surces stating it even more explicitly, and statements from people who asked an embassy directly.
Upvote:1
No such requirement applies here. Your passport simply must be valid for the duration of your stay in Japan.
According to the UK Government for your British passport: "Your passport should be valid for the proposed duration of your stay. No additional period of validity beyond this is required."
According to the Consulate-General of Japan--Melbourne: "The passport must remain valid during the period of the stay but there is no minimum period of validity required."
Upvote:1
According to timatic which the airlines use to check passport and visa validity, either your UK or Australia passport just needs to be valid on arrival.