In recent times it has been a little difficult to keep up with the increasing number and variety of datasets being released by central government in the UK. There are already around new 5,400 datasets out there but until this month the Land Registry's 'price paid' data remained closed. Unfortunately, what we'll be getting is not the entire back catalogue of price paid data, but only new data on a monthly basis. This is still a welcome development, but the release of new data only is a major drawback, as Owen Boswarva notes in this blog post.
I've used this data before and it's extremely useful and interesting (and it also allows you to find out how much your neighbours sold their house for, should you be so inclined!). Of course, you can do this already via websites like Zoopla but you can't get the entire datasets from these providers, which is only fair because they pay a lot of money for it (more than £50k). Perhaps the Land Registry will eventually release the entire dataset, going back to 1995 for England and Wales, but until then this remains a tantalising but ultimately frustrating development.
N.B. This data will, of course, be 'free' in the same way that all other datasets paid for by the taxpayer are 'free'!