What is the test for obtaining an authorization to intercept communications without a search warrant?

Later, in reaching his conclusion that Part IV.1 was constitutional, he stated, at p.78: The provisions of Part IV.1 with respect to the granting of an authorization to intercept private communications, considered as a whole, are more stringent (and rightly so) than the requirements for a conventional search warrant. As Mr. Justice Estey said in Lyons v. The Queen, supra, it is apparent from the entire scheme of the legislation that the judges play a vital role in safeguarding the public interest. They are vested with wide powers to protect the public interest and the legislative scheme contemplates that these powers will be exercised when appropriate.