Smaller parties are being warned not to strike formal coalition deals after Saturday's election.

Both National and Labour are expected to have to rely on support parties if they're in a position to form a government.

Outgoing United Future leader Peter Dunne has been a support partner for both parties.

He told Mike Hosking formal coalitions are doomed to fail, and smaller parties should instead offer confidence and supply.

"It still is difficult for the smaller parties to get oxygen as we've seen over the years but I think it's better than the formal coalition, where you have no room to move."

He said potential coalition partners usually have pre-election talks to find common ground.

"The last two elections 11 and 14, ourselves, ACT and the Maori Party had an arrangement to make sure we looked after each other in the talks."

LISTEN ABOVE AS PETER DUNNE SPEAKS WITH MIKE HOSKING