Surveillance aside, You do realize computers can aggregate data? It doesn't take 4 million agents to look at 4 million citizens (or 2 million, or 1 million...). The data can sit there and be deciphered any number of ways.
Of course I realise that - I'm just pointing out how John Key can probably say what he's saying and not be technically lying. Whether he's telling the whole truth is doubtful, of course.
But of course, it's another example of how the law lags way behind on tech matters - within 5 or 10 years an agent having to actually look at the data will be totally anachronistic. Algorithms can already find patterns more readily than humans can in many cases.
The word game is two sides of a coin.