Listening to Bernard Hickey yesterday; he was saying, last election 400k people registered in the period between voting starting and election day; and that there are currently ~70k 18-25yo's not registered.

400k is almost 10% of the total number of people that can vote.

The people who tend to register late; even on the day, are generally the working poor, those people most likely to vote against the current government; this restriction is nothing more than a cynical attempt to bias the election to Nat/Act/NZF voters.