Firstly, NZ spy agencies now have a legal duty to act "in accordance with New Zealand law and all human rights obligations recognised by New Zealand law". This includes rights not to be deprived of life and not to be subjected to torture or cruel treatment under New Zealand law as well as various international instruments. The MPS makes it clear that this obligation applies explicitly to "the sharing of intelligence, analysis and threat reporting with foreign partners". Spy agencies need to exercise due diligence and actively monitor to ensure that intelligence sharing or cooperation does not breach NZ law or make spy agencies complicit in human rights abuses, and must
decline or stop cooperating with the overseas public authority where a real or substantial risk of breach of human rights obligations (such as the prohibition of torture) is identified.
The UK government has just announced explicitly that it intends to breach the human rights of its citizens suspected of involvement in ISIS by murdering them. They have carried out such murders in the past, and clearly intend to do so in the future. This seems to have some pretty obvious consequences under the MPS: New Zealand spy agencies such as the GCSB can no longer share information with the UK on any UK citizen suspected of involvement with ISIS. Providing information on involvement will put them on a British kill-list and result in them being targeted for murder. Providing actual location details or intelligence which could result in their being located would allow such a murder to be carried out. Breaching this could result in individual GCSB staff being held criminally liable as parties to murder, in the same way that those who knowingly and willingly conspire with a murderer to locate their target would be.
In short, if they haven't already, New Zealand spies will need to cease cooperation with the UK in key parts of the "war on terror", until it disavows its policy of murder. The problem is that the secrecy around spies means that we don't know whether they have, or whether they've round-filed the MPS or are deliberately turning a blind eye to the UK's crimes in the name of maintaining their relationship with the Five Eyes. And where fundamental human rights are concerned, I just don't think that's good enough.