England & Wales:
If your family tree leads you to England or Wales, then London is a good place to start your research. This is where you'll find most of England's major repositories. Most people begin with the Family Records Centre, jointly operated by the General Register Office and the National Archives, as it holds the original indexes to the births, marriages and deaths registered in England and Wales from 1837. There are also other collections available for research, such as death duty registers, census returns and the Prerogative Court of Canterbury wills. If your short on research time, however, most of these records can also be searched online (most for a fee) in advance of your trip.
Located within walking distance of the Family Records Centre, the library of the Society of Genealogists in London is another excellent place to start your search for British ancestry. Here you'll find many published family histories and the largest collection of transcribed parish registers in England. The library also has census records for all of the British Isles, city directories, poll lists, wills, and an "advice desk" where you can get expert suggestions on how and where to continue your research.
The National Archives in Kew, outside of London, has many records that are not available elsewhere, including nonconformist church records, probates, letters of administration, military records, taxation records, association oath rolls, maps, parliamentary papers, and court records. This is generally not the best place to start your research, but is a must-visit for anyone looking to follow up clues found in more basic records such as census enumerations and parish registers. The National Archives, which covers England, Wales and the central UK government, is especially important for anyone researching members of the armed forces. Before you visit, be sure to check out their online catalog and comprehensive research guides.
Other important research repositories in London include the Guildhall Library, home to the parish records of the City of London and records of city guilds; the British Library, most notable for its manuscripts and Oriental and India Office collections; and the London Metropolitan Archives, which houses records of metropolitan London.
For further Welsh research, the National Library of Wales in Aberystwyth is the main center for family history research in Wales. There you will find copies of parish registers and family collections of deeds, pedigrees and other genealogical material, as well as all wills proved in the Welsh diocesan courts.
The twelve County Record Offices of Wales hold copies of the indexes for their respective areas, and most also hold microfilm copies of records such as census returns. Most also hold their local parish registers dating back to 1538 (including some that aren't also kept at the National Library of Wales).
In Scotland, most of the main national archives and genealogical repositories are housed in Edinburgh. This is where you'll find the General Register Office of Scotland, which holds civil birth, marriage and death records from 1 January 1855, plus census returns and parish registers. Next door, the National Archives of Scotland preserves a host of genealogical material, including wills and testaments from the 16th century to the present day. Just down the road lies the National Library of Scotland where you can search trade and street directories, professional directories, family and local histories and an extensive map collection. The Library and Family History Centre of the Scottish Genealogy Society is also located in Edinburgh, and houses a unique collection of family histories, pedigrees and manuscripts.
Go LocalOnce you've explored the national and specialist repositories, the next stop is generally the county or municipal archive. This is also a good place to start if your time is limited and you are definite about the area where your ancestors lived. Most county archives include microfilm copies of national records, such as certificate indexes and census records, as well as important county collections, such as local wills, land records, family papers and parish registers.
ARCHON, hosted by the National Archives, includes contact details for archives and other record repositories within the UK. Check the regional directory to find county archives, university archives and other unique resources in your area of interest.