Voters across the UK are set to go to the polls in a series of national and local elections as well as a referendum to decide the way MPs are elected.
Elections for the Scottish Parliament, the Welsh Assembly and the Northern Ireland Assembly will be held as will polls in 279 English councils.
The public will also be asked if they want to keep the first-past-the-post system for Westminster elections or switch to the alternative vote.
Polls open at 0700 BST closing at 2200.
In addition, local authority elections are being held in Northern Ireland while there is a UK parliamentary by-election in the constituency of Leicester South.
Contests are also taking place to elect mayors in Leicester, Mansfield, Middlesbrough, Torbay and Bedford.
The BBC weather forecast suggests that most of the UK will remain dry on Thursday with above average temperatures, but that there is a chance of rain in Northern Ireland.
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