Labour deputy leader Michael Cullen has been put in charge of ACC in an attempt to sell business on the party's plans to put workplace insurance back under state control.

Dr Cullen takes over as Minister for Accident Insurance from Labour's left-leaning ACC spokeswoman, Ruth Dyson, who has become an Associate ACC Minister outside the cabinet.

Prime Minister-designate Helen Clark said his appointment was a signal that Labour would do the job properly.

Dr Cullen, who is also Minister of Finance, Minister of Revenue and Leader of the House, said bringing ACC back under state control was "a very difficult and sensitive area."

However, he was confident Labour could deliver a significantly improved system within three years which would not raise average costs for business.

"We are going to have very heavy lobbying from big business but at the end of the day I think it has to be recognised that this was a major issue in the election campaign.

"It's clear we have a mandate across the three parties which support this Government ... for changing back to a single, central insurer."

National introduced competition into workplace insurance in July, despite Labour saying it would tear up contracts with insurers if elected.

Labour may have a delicate job keeping employers onside, as many have seen their premiums drop since competition started. It has previously argued that insurance companies are loss-leading to gain market share before increasing premiums.

Yesterday, Dr Cullen was taking a more conciliatory line. He said he was willing to look at ACC's decision to contract out case management of 4000 long-term claimants.