This isn't in any way supposed to be comprehensive. They have just assembled several datasets, obtained mainly through FoI requests. There is certainly lots of

This isn't in any way supposed to be comprehensive. They have just assembled several datasets, obtained mainly through FoI requests. There is certainly lots of land without registered title. Registration only became compulsory in the past 50 years or so, so if a property hasn't changed hands or been mortgaged in that time then it probably won't be on the register.