Electors must be on the electoral register in order to vote in elections and referendums in the UK. Electoral registration officers within local authorities have a duty to compile and maintain accurate electoral registers.
Registration was introduced for all constituencies as a result of the Reform Act 1832, which took effect for the election of the same year. Since 1832, only those registered to vote can do so, and the government invariably runs nonpartisan get out the vote campaigns for each election to expand the franchise as much as possible.