Alas, I have no such detailed knowledge. So I’ll restrict myself to a few general thoughts.
Some elements of this story are lamentably predictable:
The laughable shrieks of ‘Stalinism’ and ‘police state’; the shocking revelation that police searches are unpleasant when conducted at the home of a well-connected Good Egg; friends of the arrested man protesting their bafflement that anyone could imagine he’d do any wrong; the lack of political savvy by the police; the apparent assumption among disgusted commentators that it’s the police’s primary task to have more political savvy; the eye-rolling near-certainty that the positions of the Labour and Tory leaderships would have been reversed had the latter been in power; and the declaration by Shami Chakrabarti that “It is always dangerous to speculate about ongoing investigations, but…”
More novel, and a potentially worrying precedent for any number of people, is the peculiarity of the Home Office permanent secretary’s calling in the police rather than investigating the leaks internally.
Paulie has some good points to make about this affair, in particular that there’s a relevant distinction not just between leaks that damage national security and those that cause political embarrassment, but also between leaks made on grounds of conscientious objection to ministerial secrecy and those made on grounds of being a de facto spy for the opposition.
Although I don’t agree that Parliamentary privilege should be quite as sacrosanct as he might like. As Vernon Bogdanor says:
MPs are subject to criminal law as much as the rest of us… Their parliamentary privilege only extends to speeches in the chamber, not their offices. If an MP were accused of theft and keeping stolen goods in his office at the House of Commons, should he be exempt from a police investigation?
Whether Green’s arrest was reasonable as part of an investigation depends utterly on the specifics of the case. I dunno those.
But I do agree that Parliament (particularly the elected half of it) must be sovereign, and that while of course nobody can be above the rule of law, the law itself must be subordinate to democracy. On this tension, I can’t improve on this comment from Owen Barder:
If MPs believe that the good functioning of democracy depends on more information being made available than is currently required and allowed by law, then they should change the law, not break it.
For the police to enforce the law, as passed by Parliament, is not an intrusion of police power into democracy. Enforcing the law is the job of the police; and if Parliament doesn’t like the law then they are in a peculiarly strong position to do something about it.