From the longer Wikipedia page 
The Parliamentary Archives of the United Kingdom preserves and makes available to public the records of the House of Lords and House of Commons back to 1497, as well as some 200 other collections of Parliamentary interest. The present title was officially adopted in November 2006, as a change from the previous title, House of Lords Record Office.
Over three million records are held by the Archives in the Victoria Tower of the Palace of Westminster on 5.5 miles of shelving. Some of the most important constitutional records of the United Kingdom are stored by the Archives, including the Petition of Right (1628), Death Warrant of Charles I (1649), the Habeas Corpus Act 1679, the draft and final Bill of Rights (1689), the Slave Trade Act (1807 and 1833), the Great Reform Act (1832), and successive Representation of the People Acts.
Its public search-room is open from Monday to Friday, 9:30 am to 5 pm, and is free to the public, although appointments to visit should be made owing to limited seating space. The Archives also oversees records management for Parliament, has an active outreach programme and frequently appears on radio and TV programmes.
The website is  (checked February 2017)