Key Points:

Losing the powers of government is like being publicly castrated, says the ousted deputy prime minister.

Dr Michael Cullen, who resigned his leadership and finance responsibilities after Labour's defeat, is speaking out for the first time since the election to warn the new Prime Minister of unprecedented turbulence ahead.

"Failure to address the underlying causes of the current crisis will mean the next one will be even worse," he writes in the Listener.

His warning comes after John Key returned from his Hawaiian holiday to promise immediate infrastructure spending and support for small businesses.

But Cullen says it may be too little, too late - unless Key is willing to replace a "a toxic mix of greed, dishonesty and misplaced intelligence" with a nationwide focus on sustainability and justice.

If the new National Government does that, he says, then "it will deserve widespread support".