Earlier quoted context omitted.
The NZ anti-nuclear movement was mostly (but not completely) seen as a success against the US forcing their nuclear armed warships upon us (sailing into our harbours) during the cold war, and as a result making us a potential target. In the end one of the right wing party's lawmakers voted with the left wing party, enough to pass a law, the right wing party used this as an excuse to dissolve parliament and call a nat…
I think your history is a bit off. NZ was declared nuclear-free by David Lange's government. Describing that government as "left wing" is misleading, since the nuclear-free zone was perhaps one of the few things the traditional "left" supported. His government is mostly remembered for the introduction of "Rogernomics", i.e., the introduction of neoliberalism to NZ.
Muldoon as PM used the loss of the nuclear ships vote as an excuse to call an election, but was caught out when the chairman of the Reserve Bank came out publicly and explained what was happening to the economy, by then of course it was all too late. Nevertheless we were proud of our Nuclear Free state, even more so when the French terrorists sunk the Rainbow Warrior in Auckland Harbour (remember that the previous Labour govt had sailed NZ navy frigates into the French nuclear testing zone to protest atmospheric testing, this wasn't a new thing for Labour)