Because of the 100 year rule the 1921 census will not be available until 2021. The 1931 census returns were destroyed in the war. There was no census in 1941 because of the war and I do not expect to ever see the 1951 census which will not be available until 2051. However in 1939 there was a register of all people living in this country which was used as the basis or war time identity cards - and the later National Health Service registration numbers.
The following announcement has appeared on the FindMyPast web site:
In 1939, on the eve of World War II, the British government introduced an act that would allow them to gather vital information about the country’s population. This information would inform their decisions on identity cards, rationing, conscription and more, including – eventually – the formation of the NHS. In 2015, for the first time, Findmypast in partnership with The National Archives are publishing the 1939 Register online, providing an unprecedented insight into a country on the verge of war. We’re currently in the process of digitising all 7,000 volumes that contain the 40,000,000 entries that make up the 1939 Register. We'll be updating regularly on our blog and social media on how that process is going, so stay tuned
Looks interesting for those researching the last 100 years - but for the time being at least this site will be concentrating on local and family history before the end of the First World War.