Last month Immigration Minister Peter Dutton said the government had turned back 20 boats since it won office – an average of one a month.

The analysis said:"Arguably,boat turn-backs would not have been successful at all without the July 2013 decision … it's hard to believe that it would have been physically possible to turn back 48 boats[a month]".

It pointed to other Labor measures that helped stem the flow of boats:"enhanced screening"of Sri Lankan asylum seekers that forced many to return home quickly,and the decision by Indonesia,at Australia's urging,to stop issuing Iranians with visas on arrival.

Mr Hughes and Mr Menadue said when in opposition the Coalition blocked legislative changes that would have enabled asylum seeker processing in Malaysia,which"kept the door open for tens of thousands of boat arrivals".

Mr Menadue is a former secretary of the Immigration Department,and was head of the Department of Prime Minister and Cabinet under Malcolm Fraser and Gough Whitlam.

Mr Hughes is a former senior policy official at the Immigration Department and later advised the department on the proposed Malaysia deal.

Mr Dutton said Operation Sovereign Borders and boat turn-backs"showed the people smugglers they were dealing with a government that would be resolute in shutting down their illegal trade".

"From the moment Labor dispensed with the Howard-era border protection measures the people smugglers were in business and the boats started flowing,"he said.

Offshore processing and denying unauthorised boat arrivals settlement in Australia were policies the Coalition held in opposition,Mr Dutton said.

Labor immigration spokesman Richard Marles said the party's offshore processing policy had a"profound impact on stopping the flow of vessels between Java and Christmas Island"and an end to deaths at sea"could have been achieved much sooner had the Liberals not opposed Labor's Malaysian solution".

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