Childrens names & DoB, previous addresses, employment status, national insurance number. That info alone is enough for someone experienced to do damage.

Isn't that info relatively easy to obtain from most people anyway? Not on such a large scale of course.

You can obtain that sort of info, by dumpster diving say, but not in anything like the scale.

Imagine that you can get this info and a pretty good idea of salary and lifestyle by running a db search in a few seconds. You can easily focus your attention on the most lucrative propositions and get info from even those that are careful to not put such info out there. Census completion is a legal requirement, everyone should be on one.