On this issue about necessity and the nature of the information-sharing agreements, I don't necessarily agree that materiality is a workable test. I am saying that because I think necessity is much easier to manage.
Materiality brings into relief not only what you know at the transmitting agency but also what the recipient agency or the requesting agency knows, because under this legislation the service could request from any one of the other 17 agencies. It's unworkable to say that the transmitting agency should know the service file. We have one intelligence agency, CSIS, so if CSIS thinks.... Pick somebody else, such as the CRA or the Department of Health. Let's say that for some reason CSIS thinks the Department of Health has important information for their case. The people at the Department of Health aren't going to know the entire CSIS brief, nor is it practical for them to know it, but they would need to know that to execute on materiality.
Necessity, by contrast, I think is more modest. The service can warrant why it's important to them, and Health Canada can then do its own due diligence on its own side. Materiality is just a very broad concept that brings it into a whole mosaic that I think is just not practical for all the various agencies to transact in parallel.