Decmil has been accused of poor organisation and management after being stripped of a New Zealand prison contract but the engineering group's chief executive says fault also lies with poor design choices.

Perth-based Decmil said last week that it would take an interim loss after setting aside $50 million-$60 million in provisions for unpaid money on the $NZ185 million ($181.5 million) prison contract, which was terminated by New Zealand's Department of Corrections (DOC) on February 25.