The former United Future leader Peter Dunne says whichever government is formed after coalition talks with New Zealand First is unlikely to last the parliamentary term.
Peter Dunne said he believed there was an in-built self-destruct mechanism within New Zealand First.
The New Zealand First board and caucus are meeting again today as they try to decide whether to form a government with Labour or National.
"The fact that you built something on the basis of vanity suggests that there's going to be a point where something is going to be upset," Mr Dunne told RNZ.
"It's the vanity of the party doing the negotiating, it's all about it rather than what's in the best interests of the country and you can't build a house that way."
Mr Dunne was a minister outside cabinet in both National and Labour-led Governments.
In 2005 his party and New Zealand First supported Helen Clark's Labour-led Government with confidence and supply, with the Greens in an abstention deal.
He said the major parties should be driving the current negotiations, not a minor party.
"I think it raises the question really of the process by which the negotiations are commenced and whether we shouldn't have a system where effectively the Governor-General invites the leader of the largest party to try and form a government and if they can do so then well and good, and if not then you move to the next party, but at the moment it's very much cart before the horse."
He said National and Labour were acting as if they were scared of Winston Peters.
"That's not the basis on which to form a government, you have got to form a government on the basis of trust and some agreement about direction, not a fear of upsetting someone."