If the Government wanted to replace one of the four finalists with Red Peak, it could do so by order-in-council. But if it wanted to add a fifth alternative, it would need to change the law around the flag referendum.
Labour's policy is to support a review of the current flag but it decided to oppose the two-stage referendum proposed by Mr Key as a waste of money.
Mr Key is wary of changing the process, but has not ruled it out altogether. When asked about the popular alternative at his post-Cabinet press conference yesterday, he said he would only consider taking a bill to Parliament to add Red Peak to the ballot if it had cross-party support (excluding New Zealand First) and only if Labour backed the flag referendum process.
"They would need to go back and change their position on the flag process," Mr Key said. "Instead of lying to the public, saying they are opposed to this when their policy is actually to change the flag, if they want to treat the whole process with respect they are welcome to come and have a discussion with me but that is not the way they have played this thing. They have not played it with a straight bat."
The Cabinet accepted the recommendations of the Flag Consideration Committee as to which should be the four alternatives put to the vote in the postal referendum from November 20 to December 11. The most popular will be pitted against the current flag in a second referendum from March 3 to 24 next year.
A petition urging that Red Peak be added to the ballot is expected to be presented at Parliament today.