No matter that the ban has been blatantly ignored in the wake of the 2003 law which supposedly put it in place - and the breach of which was so embarrassingly exposed by the Kim Dotcom case.
That is just too bad. Key will argue that the Security Intelligence Service, which is legally entitled to spy on New Zealanders, increasingly cannot do its job without technological assistance from its sister agency. He may also blame Labour, saying that back in 2003 officials were under the impression the informal SIS-GCSB arrangement would be formalised and written into the new law. Funny then that National supported the ban at the time.
If Labour is unwilling - as is likely - to go along with Key's intention to overturn the ban which Labour put in place to enhance civil liberties and instead continues to press for a full and independent inquiry into the country's intelligence-gathering apparatus, Key will try to paint David Shearer as weak and flaky on national security.
Key will argue intelligence gathering and monitoring would suffer in the interim and leave New Zealand vulnerable to potentially serious threats, be they terrorist-linked or otherwise.
In flagging his intention to throw out the law forbidding the GCSB from intercepting the communications of New Zealand citizens and permanent residents, Key may or may not reveal specific examples of potential threats.
Key will argue the resulting pooling of resources is simple common sense given the cost of the GCSB's equipment and the SIS' need to have swift access to the material produced.
Key will try to sweeten Labour by promising a new and much tougher parliamentary oversight regime to keep the SIS and GCSB on the straight and narrow.
There are many overseas examples of such regimes which make New Zealand's watchdogs, the Inspector-general of intelligence and security and Parliament's intelligence security committee, look like powder puffs in comparison.
In Germany a parliamentary "control panel" reviews the legality of actions and effectiveness of all intelligence agencies. The panel handles citizens' complaints, can request information from agencies and has subpoena powers.
What Labour thinks matters as it is the only other party likely to be the majority partner in a coalition or other governing arrangement.
What is at stake is the bipartisan stance of the two major parties which has seen by and large a consensus on intelligence matters for the great bulk of the modern-day era.
It is easy for the Greens to pour scorn on how limited the oversight of the intelligence services has been during that time. But Labour has to take a more pragmatic stance. Otherwise, the structure and powers of the services would change every time there is a change of government.
Labour will have to think carefully before rejecting Key's proposals outright. It cannot let him box it into a corner. It could retain the moral high ground by offering its backing for a temporary law change subject to the outcome of a full inquiry.
But Labour will not want to let Key shift the debate. The chaos flowing from the GCSB's participation in the Kim Dotcom raid and arrest is the story which refuses to die.
It has given Labour and its allies the means to portray a different John Key by drawing all the mistakes, the miscues and memory blanks together and argue they are the manifestations of a flawed politician, rather than merely out-of-character quirks.
So last week the public was being asked to draw conclusions about Key's supposed cronyism in his appointment of an old family friend as a spy chief.
This week the question mark was placed over his competence (or lack of such) in fulfilling his obligations as the minister-in-charge of the GCSB.
There were plenty of calls during an Opposition-forced snap debate in Parliament for Key to stand down from that role on the basis that he had failed to meet his own standard and had sacked colleagues for being such failures.
No one was cruel enough to draw comparisons with Hekia Parata's performance. But the Opposition's equating of Key with other failed ministers carried some sting because there was more than a grain of truth in what the Opposition was saying with respect to Key's standard.
In Key's case, he seems to have been a victim of more pressing demands on a Prime Minister's time and the wretched condition of the GCSB as revealed by the Kitteridge report. That is not an excuse, however, for not being on top of the portfolio. He just never expected to be blindsided by it.
The concern within National over Key's trials and tribulations was clearly evident during the Wednesday afternoon snap debate. The party's speaking list included five senior ministers - Bill English, Gerry Brownlee, Tony Ryall, Chris Finlayson and Anne Tolley, the latter chipping in as Minister of Police and thereby representing the other big losers from the GCSB pulling the plug on co-operation with law enforcement agencies until the law is clarified.
Rather than further inflame things, the five ministers largely confined themselves to legal issues. They were also at pains to point out that the illegal co-operation between agencies had continued unfettered during Labour's tenure in the Beehive.
What was important was that National MPs not lose the snap debate.They didn't.
It is now up to Key to make amends to a wider audience.
