Registration of Births, Marriages and Deaths started in around 1837 with the Births And Deaths Registration Act of 1836. To facilitate the registrations many Registration Districts were established, originally corresponding to the jurisdiction of the Poor Law Unions created by the Poor Law Amendment Act of 1834, which introduced the use of Workhouses as opposed to parishes having to fund the poor in the community.
So a certificate may include the phrase “Wigan Union”, for example, but this will be shorthand for the Registration District, it doesn’t mean the person was in a Workhouse.
Over time, as populations changed, the Registration Districts diverged from the Poor Law Unions and the latter were eventually abolished in 1930.
For Poor Law Unions see Wikipedia. For a list of the Registration Districts past and present see Wikipedia.
Norman And Marian Barton Family Tree 