Elections in the United Kingdom are categorized into five main types: elections to the House of Commons, devolved parliaments and assemblies, local elections, mayoral elections, and Police and Crime Commissioner elections. General elections are held when all seats are contested, typically on a Thursday. The timing of general elections is at the discretion of the prime minister, while other elections occur after fixed periods. Various electoral systems are used, including the first-past-the-post system and the single transferable vote system. Elections are administered locally by acting returning officers.