Pseudonymised NHS data
I wrote some software a few years ago to let GPs/PCTs/CCGs/etc (ie. UK family doctors and the people who pay them and fund medical care) identify anomalies in referral patterns, hospital admissions, length of stay in hospital, "GP performance", "over-referrals" (largely a myth, BTW) and so on. It was funded and used by local GPs - ie. the NHS itself - and the base dataset was the NHS Spine data.
The software was great, but it was useless for the first year or so, because no-one would let me (ie. the GPs) see the raw data with DOBs and gender in it, and you can't do the stats without them. It took a year to get the authorisations, but without postcode (or, equivalently, deprivation) data. Much better, but you can't really be sure what's going on without post/zip code, which makes the data identifiable. I spent about a year trying to get the additional clearance, but there was so much politics in the local NHS that it was next to impossible. The whole system then imploded with the PCT/CCG changeover, and everyone's access to the data was withdrawn, and the funding went, and the NHS disappeared up it's own backside.
So, the software has been unused for 2 years, and no-one in this area (and probably any other area) has any statistically valid way of finding out what's going on in primary care. The govt has now apparently decided that this is important again, so other people are now going to spend a couple of years dicking about trying to get the Spine data, before losing it again. And the whole pointless cycle will repeat again in another 5 years. And the base Spine dataset cost going on for a *billion* to create, plus maintenance.
So, if you're worried about the privacy of your NHS data - don't be. Everyone in charge is so stupid and paranoid that no-one's ever going to see it anyway.