Sorry to be dim but which register are you referring to?
The 1939 register is on Findmypast which is a pay per view site. You can buy credits.
The National Register taken in 1929 listed the personal details of every civilian in Great Britain and Northern Ireland. This Register was a critical tool in coordinating the war effort at home. It was used to issue identity cards, organise rationing and more.( I still have mine)