Australia's self-styled role as policeman of the South Pacific was delivered a serious blow yesterday when its law-and-order mission in Papua New Guinea was declared unconstitutional by Port Moresby's highest court. The 200 Australian police and public servants who have been working in PNG for the past six months were immediately stood down, and will likely return home. Canberra fears its former colony could spiral into chaos due to a potent mix of poverty, unemployment, tribal tensions and a HIV/Aids epidemic. The deployment was part of a post-9/11 strategy by Canberra to prop up ailing states in its immediate region to prevent them becoming havens for terrorism and transnational crime. Australian Foreign Minister Alexander Downer described the ruling as 'without doubt a setback', saying a decision on whether to withdraw the contingent would be made in the next few days. The 161 police were packing their bags in anticipation of a swift withdrawal. In a unanimous verdict, five Supreme Court judges upheld a legal challenge to the mission, ruling as invalid the immunity against prosecution enjoyed by the Australian police, which Canberra had set as a proviso for the five-year, A$800 million ($4.78 billion) Enhanced Co-operation Programme. The legal challenge was brought by one of PNG's provincial governors, Luther Wenge. He accused the Australian police of breeding resentment by driving around the crime-plagued capital in new four-wheel-drive vehicles, while local police struggled with poorly maintained cars and a shortage of firearms. 'People are complaining the Australians are too patronising - that, we don't want. We are brothers, we are comrades,' Mr Wenge said, calling on both sides to renegotiate the deployment.