The government has been accused of trying to cover up financial mismanagement at the Ministry of Health.
The ministry budgeted $24 million for a head office refit in 2014, but later had to ask the government for an extra $18m after what it calls a forecasting error.
In question time, Labour leader Andrew Little asked the prime minister how two of his ministers could have signed off on the Ministry of Health's budget - knowing it didn't have the money to pay for its office refit.
Mr Key told the House that he had full confidence in them.
But Labour deputy leader Annette King said the government has tried to keep the financial mishandling at the ministry a secret.