How often do our spies do police work?

Back in August, when the possibility that the GCSB were working for the copyright mafia first arose, I drew attention to section 8(2)(c) of the GCSB Act, which allows them to perform their function (tapping phones and hacking computers) "in support of the prevention or detection of serious crime". As it turned out, "serious crime" wasn't so serious - it meant "anything in the Crimes Act" - including burglary, bigamy, and blasphemous libel. The SIS has a similar dodge, allowing them to retain information and pass it on to police "for the purpose of preventing or detecting serious crime" - which has a similarly broad meaning. Which raises the question: how often do our spies do this, and use their powers effectively to aid the police? What restrictions are there on it? Is there a threshold of seriousness before they will (ab)use their powers in this way, or do they just help out whenever the police ask?

These are important questions. Our police are rightly subject to tight restrictions on their use of surveillance. Our spies are not (and have lax Ministerial oversight to boot). If the police are systematically circumventing the restrictions Parliament has placed on them by going to the spies, we need to know, so we can decide if its really what we had in mind. And if they're going beyond what Parliament envisioned, then some emasculation may be necessary.