Normally it’s 100 years before a British census is available, to ensure none, or very few, of those mentioned in it are still alive. However, a 2006 ruling by the Information Commissioner has meant that the census information for England and Wales has become available from the National Archives sooner than the projected January 2012 release date.

Although searching the census – the first to have data written by the participants themselves – is free, viewing and copying images is on a pay-per-view basis. Not all data will be available yet; information deemed “personally sensitive,” meaning “details of infirmity or other health-related information, information about family relationships which would usually have been kept secret and information about very young children who were born in prison,” still won’t become available until 2012, and nor will data from Scotland.

The site currently offers data on 80% of the people in the UK on April 2, 1911. The coming months will see information on another nine million people released.

When the 1901 census was released in January 1902, demand was far higher than anticipated, and this time organizers were ready, with 26 servers available. Checks during the day showed that, although slow, the site didn’t crash.