The man who will head the Turnbull government’s Home Affairs department has launched a scathing attack on critics of the new portfolio amid concerns it will constitute a “sinister behemoth”.

Announced in July, the controversial new portfolio has been labelled “politically motivated” and described as “empire building”.

But Mike Pezzullo, currently Secretary of the Australian Department of Immigration and Border Protection, defended the shakeup on Monday, saying claims it was overly bureaucratic and would concentrate too much power in the hands of officials were wrong.

“(Any) suggestion that the establishment of Home Affairs will somehow create an unchecked, extra-judicial apparatus of power is ill-informed … fallacious, and unworthy,” he told a Senate Estimates hearing.

The new portfolio will combine agencies and functions originally held by  Immigration and Border and the Attorney-General’s department: Immigration, ASIO, the Australian Federal Police, Austrac and the Australian Criminal Intelligence Commission.

It was thrown into the spotlight last week following a speech Mr Pezzullo gave in which he outlined the Home Affairs’ “philosophical context”.

Prime Minister Malcolm Turnbull and Immigration Minister Peter Dutton unveiled the changes in July. Photo: AAP

He said the state would need to “increasingly embed itself” into “global networks and supply chains, and the virtual realm, in a seamless and largely invisible fashion, intervening on the basis of intelligence and risk settings”.

That was because there are “global dark markets for hacking, money laundering, cryptocurrency movement, assumed identities for criminals, terrorists, child exploitation perpetrators and others”.

‘More about politics’

Immigration Minister Peter Dutton is the big winner from the bureaucratic shakeup, but critics say the move will put too much power in the new Home Affairs Minister’s hands.

John Blaxland, a prominent national security expert at ANU, wrote in July that “this is more about politics than substantive fact-based organisational reform”, describing it as a “fraught move”.

Labor has not stood in the way of the changes, but asked the government to “justify the biggest overhaul in 40 years”.

Mr Pezzullo said on Monday the department would still be subject to oversight from the Parliament and bound by the law.

He added that some of the agencies, such as the Australian Border Force, would operate independently from the the new department.

Existing arrangements for the oversight of ASIO, federal police, Australian Border Force, Australian Criminal Intelligence Commission and financial intelligence watchdog won’t change, Mr Pezzullo said.

“The core functions of this department will be policy functions and planning, in relation to domestic security, law enforcement, counter terrorism, the protection of our sovereignty and the resilience of our national infrastructure and systems,” he said.

-with AAP