How often do police spy on our TXTs? They don't know

Last week I highlighted some problems around the use of production orders by police. Police can use these orders to obtain both call-associated data (such as who you called and where you are) and stored telecommunications (including text messages and emails) from phone companies and ISPs. But there is no protection for legally privileged material, and the orders can be used to gain this information for trivial offences such as disorderly behaviour and resisting police. So how often do police use these powers? According to an OIA request someone filed through FYI, they don't know:

Police apply for Production Orders pursuant to the Search & Surveillance Act 2012 for a full range of criminal offences punishable by imprisonment, for example crimes of violence, dishonesty and drug offending. We do not collect information on the numbers of production orders, how many were granted or declines, the categories of offences or the type of documents (including CAD or content) sought because we have no business reason nor requirement in the Act to report on this activity.

Which is simply incredible. This is supposedly a major tool for crimefighting (and I agree, it is, and is perfectly justified for serious offences), but they have no idea at all how it is used. And when we're talking about a major intrusion into privacy - one that would require a predicate offence with a penalty of seven years imprisonment if the information was captured in real time rather than off a server - that's just not good enough.

And for an example: the police appear to have used this power (or otherwise obtained call-associated data) in the recent sleep-driving case, for which the predicate offence would seem to be driving while impaired. While not wanting to discount the seriousness of drunk driving, I'm not sure that its what we had in mind when we gave the police this power.