Tim.
Legally you may have access to many records at their repositories(but records of a personal nature may not be accessed for anything between 30 and 100 years.)That doesn't mean you can see them online anywhere in the world. In addition there are statutory fees for copies of some records
You can freely visit the National Archives . This holds the census, the 1939 register mentioned above, medal rolls, older PCC wills WW1 service records( + lots more) Local archives often hold church registers so these are usually freely accessible at the archives. However, if a C of E register is still in the church then the set search fee is at present £31 an hour. A few local archives apply this fee if you want a copy. (they will send you a certified copy)
You can freely view the National index of wills and probate and of post 1837 births, marriages and deaths but these are very limited in the information provided.
Beyond that, there is frequently a cost. The National Archives, Kew, commercialises popular records such as the census. Consequently, there are no images of any census on any free to view site. The recent thread on the 1921 census shows just how much it will cost those who can't visit Kew to view. (the money received does help fund archival costs so helps preserve other records). Other local archives operate similar models for their parish and other popular records. That's why so many are only available on subscription sites.
In addition, if you want a full birth, marriage or death cert, it will cost you £11.https://www.gov.uk/order-copy-birth-death-marriage-certificate
If you wanted a post 1858 will you could visit First Avenue House, in London. You can see the will without cost but you can't transcribe it.( last time I visited, there were big notices all round reminding you. I had to restrict the number ordered because of the relatively high cost of copies.) This cost has been reduced considerably with recent online availability but they still cost £1.50 each.