It seems to say you need one whichever country you put in.
Thanks everyone for the comments about NZ.
As tmg513 says, the tool on the Post Office website claims you'll need an IDP whatever country you enter. The caveat is further down the page: "
... ask the [rental] company concerned to confirm the driving licence requirements of the countries you’re visiting. Without this info, consider an IDP as a precautionary measure."
Wikitravel says: "
You can rent a car in New Zealand if: You're over 21 years old and the holder of a valid international drivers' licence or a current local licence. Drivers with a full driving licence can drive for 12 months from the date of arrival".
It seems to me the IDP is like the passport checking service, another Post Office money-making venture.
~ian
