The main historic records of the criminal justice system can be found in the National Archives and local record offices. The National Archives (TNA) holds the records of the Home Office (HO), Metropolitan Police (MEPO), Assize (ASSI – although local assize records are held at regional record offices) and Prison Commission records (PCOM). Records relating to convict transportation can also be found amongst the Colonial Office (CO) and Admiralty (ADM) records. The National Archives holds a huge range of records available, many of which are also now digitised and available from www.findmypast.co.uk.
The best way to explore what is available at TNA is by using their excellent online guides. For example: Criminals and Convicts, Criminal Trials in the Assize Courts, 1559-1971 and Police. Local Record Offices also hold some criminal justice and policing records. For example, these include local and regional police and constabulary archives, records of the court (Assize, Quarter Sessions, Petty Sessions or Magistrates court), local prison archives and reformatory and industrial school archives.
Survival and access can vary from archive to archive. Many record offices have excellent online information online (for example, the West Yorkshire Archives Service and the East Riding Archives Service). Before you visit an archive make sure you read the guidance on the website. Many allow you to register and even order in advance, so it is worth doing some initial preparation before you go. Archive staff are usually happy to answer questions although you are advised to contact them in advance of your visit, especially for more complicated queries (see the Researching Here section for getting started at TNA).