Yet again the Australian National Audit Office has exposed the cost of the Labor-Greens alliance in government and their decisions to throw open Australia's borders to the people smugglers and 50,000 illegal maritime arrivals (IMAs).

Labor re-established Regional Processing Centres (RPCs) in Nauru and Papua New Guinea in sheer panic in 2012 when it finally realised its 'open border' policy was overwhelming the nation's ability to cope with growing numbers of boats carrying thousands of IMAs each and every month.

The Greens must equally share the blame for the disastrous border policies they urged upon Labor. To this day they still believe in open borders – just ask Senator 'Sea Patrol' Hanson-Young or her underwhelming replacement.

Labor and the Greens have never taken the responsibility for the chaos and costs they inflicted on the Australian people.

But they cannot escape this latest expose of their border policy failures.

The simple fact is there would be no IMAs in Nauru or Manus had Labor maintained the Coalition's Howard-era policies of border protection.

Nor would Labor have had to open 17 detention centres within Australia.

Eight thousand children would not have been put in detention.

Twelve hundred people would not have drowned at sea.

It took a Coalition Government to stop the boats, to end the deaths at sea, to close those 17 centres and to remove all children from detention.

The 30,000 legacy caseload of IMAs in Australia and the RPCs in Nauru and Manus are a Labor-Greens legacy.

Australians should never forget the cost of that legacy – an $11 billion budget blowout.

The Coalition was left the unenviable task of cleaning up Labor's mess. We have returned integrity to our borders and our refugee and humanitarian programmes.