The comedy writer told ShortList that the fourth series of the political satire would reflect the current coalition government in the UK.
Iannucci said: "We haven't started the physical act of writing it yet - we're about to get going - but we've got a storyline worked out. The third series ended with the election called and the opposition ready to take over. Obviously now we need to introduce a third party.
"If Peter Mannion [Roger Allam] is in power at long last, finally has his hands on the levers, he'll be mightily p*ssed off that there's suddenly someone else in his office, from another party, interfering.
"And no sooner do they arrive than they're told to cut their budget by 30%. Plus we'll see Nicola Murray [Rebecca Front] in opposition."
Asked if Peter Capaldi's character Malcolm Tucker will be trying to bring down the coalition, Iannucci said: "Yes, but he'll also be looking for The One.
"He's convinced there's a great new leader of his party out there. Whether he'll find The One or get shackled with The Other One, who can say?"
> Armando Iannucci confirms 'Veep' script