John Key says it would be more likely he'd take a trip to outer space than Winston Peters holding a co-prime ministership role in the next Government.
One year on from the general election, the latest 3 News/Reid Research poll has the New Zealand First leader holding the balance of power again should there be another nationwide vote.
The poll shows Labour and the Greens with 52 seats and National and its typical partners holding 60 in a 121-seat Parliament.
New Zealand First has nine seats in the House, which once again leaves Mr Peters as the kingmaker.
During an interview with The Nation at the weekend, Mr Peters didn't rule out wanting to be Prime Minister.
But the current Prime Minister doesn't think a co-prime ministership would be an option.
"More chance of me holidaying on the lunar space station I would've thought," he said at his post-Cabinet news conference today.
"There's no chance.
"It'd be totally unacceptable to the New Zealand public. Being Prime Minister is not something that is traded away with a bit coalition partner to get them over the line."
Mr Key wasn't sure how that would even work.
"He could take the weekends? Give me the time off, it'd be quite nice. Outside of that, I don't see it working. It's a joke."
The poll, taken from September 8-16, has Mr Peters on 8.6 percent as preferred Prime Minister, with Mr Key on 39.5 percent.