Voting is under way in a historic referendum on whether the UK should remain a member of the European Union or leave.
A record 46,499,537 people are entitled to take part, according to provisional figures from the Electoral Commission.
Polling stations opened at 07:00 BST and will close at 22:00 BST.
It is only the third nationwide referendum in UK history and comes after a four-month battle for votes between the Leave and Remain campaigns.
The referendum ballot paper asks the following question: “Should the United Kingdom remain a member of the European Union or leave the European Union?”
Whichever side gets more than half of all votes cast is considered to have won.
The weather forecast for polling day is mixed.
There have been thunderstorms in London and south-east England which caused flooding overnight.
Kingston upon Thames Council in south west London has moved two polling stations after they were inundated with water.
Sunshine and heavy showers are forecast for Northern Ireland and Scotland but it is set to be drier and brighter elsewhere.
After the referendum polls close, sealed ballot boxes will be collected and transported to the count venue for each of the 382 local counting areas.
These represent all 380 local government areas in England, Scotland and Wales, plus one each for Northern Ireland and Gibraltar.