The UK free-to-search census index is useful, but it's pay-to-view the census form or a transcript of it. I object to having my family's census information sold back to me. Our relatives filled out these forms for free, and the government used the information for their own purposes at the time.
There are four counties not online, including Northumberland and part of the West Riding of Yorkshire. If you don't find your ancsestors, they might have been on the 12-15% not yet online.
The 1911 census of Ireland is also online - for free, including downloadable copies of the original census page, and other enumerator information. *That's* the way our family information should be available. There are only four counties online so far including Dublin, but counties are being put online progressively over the next 6-12 months. I was amazed to find it online last night.
The Irish government is finally coming up with family information we need, at no cost, the same way our ancestors provided the information to the government in 1911. Good on them.
Debbie