Mr Dutton on Thursday said it has been a year since a successful operation by "evil people smugglers" seeking to bring asylum seekers to Australia. The last boat containing 157 Tamil asylum seekers who had fled Sri Lanka arrived in June last year. It was intercepted near Christmas Island and the passengers were detained on a Customs boat for a month, before being transferred to the Curtin detention centre, then Nauru. Since December 2013 when the turn-back policy began, 633 people on 20 boats have been turned away and thousands more dissuaded from making the perilous journey to Australia, Mr Dutton said. "If people smugglers see ventures getting to Australia successfully, that is a green light for the people smugglers to be back in business," he said. "We are not going to allow the deaths at sea to recommence."

The government has previously revealed that 12 boats arrived in the six months to May last year. It means eight boats have been turned back in the past 14 months, indicating the rate is slowing. It is widely accepted that the turn-back policy, described as cruel by critics, has dramatically stemmed the flow of asylum seeker boats headed to Australia. At Labor's national conference last month, Opposition Leader Bill Shorten headed off an attempt by the Left faction to amend the party's platform to prohibit a future Labor government turning boats back to Indonesia. Labor frontbenchers Anthony Albanese, Tanya Plibersek and Penny Wong opposed the move – division the government has seized on to claim the party lacks conviction on the issue. On Thursday, Mr Dutton said Labor was "split down the middle … you need to have the resolve to stare these people smugglers down and the Abbott government has had that resolve".

Mr Dutton confirmed 46 people on a boat from Vietnam were returned last month – the government's first admission of the boat's existence. Late last month, Prime Minister Tony Abbott would not say if the government was in talks with Vietnam about the return. Mr Dutton said on Thursday Australia had "negotiated their return". "We have been able to stare down that venture and it's a significant outcome," Mr Dutton said, adding the operation was a "good outcome for the sovereignty of our nation." Greens senator Sarah Hanson-Young said there were no guarantees the Vietnamese asylum seekers were safe.

She said disclosing the number of asylum seekers turned back "proves nothing but how callous these policies are by sending people back to danger". "If the government wanted to be honest about what is really happening on the high seas, they would tell the Australian people what happened to the people who are turned back," she said. "The government trumps turn-backs as saving lives. But ... it merely forces people back to unsafe situations where they are faced with other life-threatening dangers." Follow us on Twitter