A former immigration department head has dismissed as "futile" the coalition's insistence on returning to Howard-era asylum seeker policies.
John Menadue, who was the department's secretary under the Fraser government, says reopening the detention centre on Nauru would not work again.
It did not work before because, while the number of asylum seekers arriving by boat declined, the total arrivals remained consistent, he said.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
The coalition maintains the only way to stop asylum seekers coming to Australia without waiting for refugee visas onshore is to reopen the offshore processing centre in Nauru, reinstate temporary protection visas and turn back boats.
"I think that's a very dishonest argument because asylum seekers continue to come by air," Mr Menadue told ABC radio on Wednesday.
"It's just futile in my view to continue with one-liners and slogans about Nauru."
The opposition had a "phobia about boats" even though three-quarters of asylum seekers came to Australia by air.
Mr Menadue also attacked coalition immigration spokesman Scott Morrison for his recent scare-mongering about refugees on boats bringing infectious diseases into Australia.
"That is a disgraceful proposition and Scott Morrison should withdraw it," he said.
An infectious disease physician, Trent Yarwood, last week wrote an open letter to Mr Morrison saying his claims were "not supported by publicly accessible health data" and vastly over-emphasised the risk to the general population.
Mr Menadue said he did not have any political agenda and was not a member of any political party.
