The UK has voted by 52% to 48% to leave the European Union after 43 years in an historic referendum, a BBC forecast suggests.
London and Scotland voted strongly to stay in the EU but the remain vote has been undermined by poor results in the north of England.
Voters in Wales and the English shires have backed Brexit in large numbers.
The pound fell to its lowest level against the dollar since 1985 as the markets reacted to the results.
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The referendum turnout was 71.8% – with more than 30 million people voting – the highest turnout since 1992.
Labour’s Shadow chancellor John McDonnell said the Bank of England may have to intervene to shore up the pound, which lost 3% within moments of the first result showing a strong result for Leave in Sunderland and fell as much as 6.5% against the euro.
UKIP leader Nigel Farage – who has campaigned for the past 20 years for Britain to leave the EU – told supporters “this will be a victory for ordinary people, for decent people”.
Mr Farage – who predicted a Remain win at the start of the night after polls suggested that would happen – said Thursday 23 June would “go down in history as our independence day”.