What's the argument for the SIS's new video surveillance and urgent warrantless search powers? They won't say, but from the comments of the committee, its clear that they've been told in their secret briefing that the powers are to stop terrorism. One of the National MPs (I think it was committee chair Mark Mitchell?) was explicit, asking a submitter about the prospect of a Woolwich-style attack, "a New Zealand serviceman walking along the street, being cut up with meat-cleavers and machetes" (paraphrased). Clearly, they expect the new powers to be used to directly prevent such attacks, with the SIS using urgent warrants and video surveillance to gather the required evidence to prevent it.
But there's a problem: legally, the SIS cannot act to prevent such an attack. The SIS's core function (as laid out in its governing Act) is "obtain, correlate, and evaluate intelligence relevant to security". However, that Act also says that
It is not a function of the Security Intelligence Service to enforce measures for security.
What's "enforc[ing] measures for security"? An IGIS report from earlier this year gives an example. The SIS had delivered a "warning" to a man they (incorrectly) believed was conspiring to assassinate a foreign head of government. The Inspector-General found that this contravened the Act and ordered the SIS to cease the practice until they had received advice from Crown Law on its legality.
And this makes sense. The SIS are not the police. They are there to gather intelligence, while the police are there to protect public safety and prosecute criminals. "Measures to enforce security" - disruping terrorist attacks, arresting spies - fall into the latter category, not the former.
So what should the SIS do if they gain intelligence suggesting a terrorist attack in New Zealand? Turn it over to the police. Section 4H of the SIS Act allows them to provide the police with information on "serious crime" (anything punishable by two years imprisonment, so burglaries and minor assaults apparently qualify), and the police have urgent search powers of their own they can then use. The police can gain all the information the SIS would hope to gain, except with legal oversight and full admissibility in court, allowing would-be terrorists to be prosecuted.
In short: the SIS does not need these powers, and cannot use them for the purpose they're selling them as being useful for. And if they have actually told the committee that they're for stopping terror attacks (rather than, say, gaining blackmail on people they wish to turn into informants), then they've lied to the Committee and need to be prosecuted for breaching Parliamentary Privilege.
(Yes, I have sent in a supplementary submission about this; I didn't realise it until halfway through the hearings)