I’m mildly opposed to National’s asset sales policy, but the reality is that they campaigned on a fiscal plan that hinged on revenues gained from the sales of assets. It would be unethical to abandon that plan the second they’re re-elected. Also, this is a proportional democracy. If they have a majority in the house then government’s can pass whatever they want, no matter what the polls might say. We then hold them accountable during the subsequent election.
If Labour really wanted to queer the deal they could go nuclear: promise a pseudo re-nationalisation; if re-elected they will pass legislation returning ownership to the state, paying shareholders out on the value of their equity based on the share-price when it first went to market.