For those waiting for the curtain to go up on the Winston Peters Revival Show, John Key has a simple message: there ain't going to be any such show. Not if he can help it.

By (again) flatly refusing to be party to any government that includes Peters, Key could conceivably find himself having to walk away from the prime ministership even though National is likely to win a landslide victory.

Such a scenario is unlikely, however. Yesterday's audacious declaration - astutely timed for the very start of election year rather than the election campaign - has the purpose of making it even more difficult for New Zealand First to return to Parliament after its three-year absence.

Key is trying to paint himself as a new kind of politician - one who is open and transparent. But there is also some pretty old-fashioned brute politics at work.

Rather than sitting and fretting as National's perennial nemesis breathes fresh life into his party, Key is operating on the principle that even though your enemy may look dead and buried, it is always best to make sure.

For the parliamentary mathematics may be complex, but the potential outcomes are very clear.

If NZ First does not reach the 5 per cent threshold, National on current polling could govern with the help of some combination of the Maori Party or Act or United Future, presuming the last two make it back aswell.

If NZ First does breach the threshold, the chances of a Labour-Greens-NZ First governing arrangement strengthen considerably.

Peters, however, already faces an uphill struggle in beating the threshold. Key has sought to make that task even harder by neutering Peters' role as kingmaker. You are not much of a kingmaker if there is only one potential king you can support, in this case Phil Goff.

NZ First loses its marketing appeal as a moderating force if one of the bigger parties refuses to play ball. NZ First's leverage with the one that will play ball (Labour) is correspondingly reduced. NZ First becomes merely an adjunct of Labour. Labour is once again tainted by association with Peters.

To that end, Key will repeat endlessly that a vote for NZ First is a vote for a Labour government, while a vote for Labour means Peters could end up with his feet back under the Cabinet table.

It all leaves Goff with an awful dilemma. He could have matched Key's refusal to work with Peters. The trouble is a resurrected NZ First offers Labour its best hope of returning to power and Goff becoming prime minister.

Key's mischievous matchmaking, however, has him defining the election as a contest between a forward-looking National Party versus a rearwards-looking Labour Party beholden to the whims of NZ First.

In short, Key's not-so-subtle pitch is one of stability versus chaos. New Zealand, you choose.