Primary sources
https://www.british-history.ac.uk/catalogue/primary-sources
Secondary texts
https://www.british-history.ac.uk/catalogue/secondary-texts
Datasets are born digital materials that have been edited and prepared by historians. British History Online has transformed the original databases into web pages.
https://www.british-history.ac.uk/catalogue/datasets
Historic maps of London from before 1800 and maps from the 19th-century series of the Ordnance Survey, including the complete 1:10,560 series and selected areas of the 1:2,500 maps. The Ordnance Survey maps can searched by keyword, title or postcode
https://www.british-history.ac.uk/catalogue/maps
Calendars are summaries of documents arranged chronologically, intended as a finding aid like an index or a library card catalogue. In many instances the summaries are very detailed, such that the researcher does not need to consult the original documents; however if you would like to consult the originals, they are often held at the National Archives at Kew.
https://www.british-history.ac.uk/catalogue/guides-and-calendars