The outgoing head of the Australian Security Intelligence Organisation (Asio), David Irvine, has compared intelligence agencies’ use of metadata to “looking up a telephone book” and says requiring a warrant for metadata access would cause intelligence gathering and law enforcement to “grind to a halt”.

The federal government is preparing laws to force telecommunications companies to keep metadata for two years, clarifying – after early confusion – that the data retained would include subscriber, identification and location information, but not web address identifiers. The information can be accessed by a large number of government agencies without a warrant.

In an address to the National Press Club the head of the normally secretive organisation pleaded for debate over the law changes to “avoid paranoia, including evoking the spectre of Big Brother, 1984, mass surveillance and mass violations of privacy.”

Asked why warrants should not be required to gain access to metadata, Irvine said it was impractical, because metadata was used so often, including to gather enough information to decide whether to seek a warrant in order to then monitor the content of a subject’s communications.

“For law enforcement and for security intelligence the ability to know when one of your targets is communicating, and with whom, is of crucial importance … in giving you the groundwork to decide whether you want to go to more intrusive methods like warranted interception,” he said.

“We have been using metadata, as it seems to be called these days, for many years and we use it on a targeted basis, so we are not out there exercising mass surveillance … but we use it very frequently. We use it as frequently as any of us in the old days used to go and look up a telephone book. But we don’t have telephone books in the same way for all of this sort of stuff and yet we need this kind of information. Now if you are going to ask me for a warrant every time I have to go and look up a telephone book … with three or four or five pages of justification … then not only is Asio going to come to a halt but all the law enforcement in Australia is going to come to a halt,” Irvine said.

Irvine, who will step down in September, was speaking three weeks after the government announced a dramatic expansion in its anti-terror powers in response to the future threat from returning jihadist fighters, to be implemented in stages.

Laws to implement the first stage are already before parliament, including new powers for Asio to carry out surveillance on multiple computers and entire networks and much tougher penalties for the disclosure of intelligence material which could potentially include journalists – to the consternation of many media companies.

New border security measures

New customs and border protection counter terrorism units have already begun operating at international airports, and have intercepted “at least one person of interest,” prime minister Tony Abbott announced on Wednesday.

Speaking during question time, Abbott said the units were already in place at Sydney and Melbourne and would soon be established in all international airports across the country, alongside already announced measures such as biometric security.

“An additional 80 Border Force officers, stationed at international airports will monitor movements of people on our national security watch list,” he said.

“I’m advised that these new units have already intercepted at least one person.”

The man was arrested heading to Lebanon from Melbourne airport.

The foreign minister, Julie Bishop, confirmed 15 Australians had already been killed fighting in Iraq and Syria, as well as two Australian suicide bombers.

The second stage is the yet-to-be-detailed counter terrorism (foreign fighters) bill which will include a new offence to ban travel to areas designated by the government as places where terrorist organisations are fighting, if the traveller cannot show they have been there for a legitimate purpose.

Irvine made it clear that the laws are a long way from being finalised, and suggested that while the onus of proof may be reversed for the law enforcer’s investigation of suspected returning jihadist fighters, the authorities would still have to prove that a suspect had been a fighter if charges were laid.

He said there would have to be a court process, and before he could answer a question about how the onus of proof would work “we need to see what the government actually comes up with” because at the moment the proposal was only available “in principle”.

“The issue has always been the problem of collecting evidence overseas that will meet the evidentiary standards of Australian courts. The use of control orders may be an option. It has been used in Australia in the past, as you know. It may need to be used again. But again, that will have to be fought out in the courts as well,” he said.

Earlier in the day Bishop had insisted there would be no reversal of the onus of proof.

“We are warning Australians not to go. We want to introduce an offence for people to go to designated areas. If they have a reason for being there, a legitimate reason, then they can go. If they don’t, then the onus of proof is on the authorities to show they don’t have a legitimate reason for being there. There’s no reversal of the onus of proof,” she said.

At the time the changes were announced the attorney general, George Brandis, said “one proposal which we are considering is the capacity for the minister for foreign affairs to certify that a particular region or a particular conflict within a region is a region for the purposes of the foreign incursions legislation, so that if it is demonstrated that an Australian has returned from that region, there can be a presumption that they were there for no good purpose.”

He also said “... there are sometimes evidentiary problems. You’ve got to be able to prove that these people have committed that offence, and that’s one of the aspects of the law we’re looking to reform: to make sure that it is easier to prove that these people whom we suspect of engaged in foreign war fighting, have in fact done so.”

Before any case was brought, Irvine suggested suspected returning fighters might be subject to the government’s existing “control orders”, which can require terrorist suspects to live in a certain place, wear a tracking device, regularly report to authorities or not communicate with certain other people.

Other measures in the government’s proposed anti-terror legislation include:

• Broadening the criteria for banning a terrorist organisation to cover not only groups engaging in terrorist acts but also those that support and encourage it – including via social media.

• Lowering the threshold for arrest without warrant for terrorism offences.

• Making it easier for the government to suspend passports.

• Removing any end date on search and seizure powers, first introduced in 2005 under an agreement between former prime minister John Howard and the states that was due to expire next year.

• introducing a new offence to travel to areas designated by the government as places where terrorist organisations are fighting, without a legitimate purpose.

Labor has indicated a general willingness to consider the new laws, but wants to see the detail rather than give the government a “blank cheque”. From the time of the announcement, crossbench senators, including David Leyonhjelm and Bob Day, have indicated they have concerns based on libertarian grounds.