Both the Conservative Party and the "Socialist Worker" are seeking to answer the same question but clearly from quite different ends of the political spectrum. One believes that by doing so it will "release massive value from our land that currently is simply not realised" and the other is concerned that 36,000 people own over half the land in the Country.
The Land Registry is the place to go to ascertain who owns what but only about 80% of land is "registered". The balance isn't simply because it hasn't changed hands since land registration became compulsory in 1990. There are other sources where land ownership can be deduced but these are not definitive and it would take considerable time and effort to achieve. In addition if you wanted to find out who does own the 80% then you need a large cheque book and a lot of time given the vast number of registered titles.
In some ways I like the Conservative Party's aspirations as amassing current and accurate data, good information always has its uses. Combine land ownership with a myriad of other data sources and I am sure you will have data which is of value. However it would be a tricky task to complete. Unregistered land is dependant on the owner having the title deeds to "prove title". These deeds can be ancient and often rely on descriptions (as opposed to plans) to describe what is owned. That is before you complicate the matter with mineral interests, rights of light, riparian and other many rights granted in the dim and distant past. Yes other countries have a complete register but it takes some commitment and resourcing. There is even a name for it, a Cadastre.
Once this piece of work is completed, which will probably take somewhat longer than a term of office, what exactly are they going to do with the information? There are campaigners who argue that by not knowing who owns land constrains housebuilding. There are concerns that for example house builders are "landbanking". The Tories say that complete land registration and amalgimantion of data from other agencies with release "massive value". How exactly? Others want land ownership to be more balanced and not have significant landholdings owned/controlled by a small number of individuals or corporate bodies.
Ascertaining who owns what seems to be only piece of the jigsaw. Simply knowing who owns a piece of land isn't really going to change anything. Whether you want to return the land to the masses that isn't going to happen voluntarily so I assume the promoters of this would want some form of right to buy or compulsory purchase. If you want to "release value" or build more houses or any other form of development then you need planning permission which is a completely different matter. Even with planning you still need a willing buyer and a willing seller.
So in conclusion it is anyones guess how long this initiative will take to complete but when done it sounds as if all parties will be happy. To acheive their ultimate goals though this would only be the start. One final point I guess that much of the "20%" unregistered land is made of of hills, mountains and moors, forest or areas for military training - not exactly house building territory?