So you're saying it's still at the discretion of a single magistrate?

I'm sure China could find some judges to rule in the name of national security if it would give everyone warm fuzzies.

Judicial checks and balances only function when they're independent of the executive and parliament

An interesting observation of the West is that people have an innate trust in the authorities/institutions. It's largely because the institutions have been well run for so long. But as that fades we're left in this twilight zone where you can point to a law like it prevents something. As is often pointed out, the Soviet constitution was much more free than the US one. Even the Romans knew this distinction

The standard of proof is reasonable grounds, don't forget your passwords because this is an incredibly low bar to pass.

>in preventing or detecting crime

If the police are requesting a s.49 notice it goes without saying that it will be for preventing or detecting crime, but notices can also be issued to ensure the exercise or performance of public bodies, statutory powers, or statutory duties without such a requirement.

>Disclosure is proportionate.

In regards to what is sought to be achieved by the disclosure. It is not disproportionate to request disclosure for the purpose of preventing or detecting crime regardless of how benign that crime is.

>If the protected information cannot be obtained by reasonable means.

The law has been used against people for failing to give up Facebook passwords. The police routinely ask companies for information without a warrant and they're usually legally denied such requests based on GDPR grounds. 'Reasonably practicable' means nothing if it can be bypassed by police trying their luck without a warrant.