The prime minister says she will move a motion for an early election in the House of Commons tomorrow, for MPs to vote on. It will require a two-thirds majority to be carried. 
Theresa May says that the only way to “guarantee certainty and stability for the years ahead is to hold this election and seek your support for the decisions I must take”.
Versus the euro, the pound slumped more than 0.4% to trade at 1.175, losing previous gains of more than 0.1%.
As a result, the next general election is not scheduled to happen until 2020.
BBC assistant political editor Norman Smith says broadcasters usually know what is about to be announced, but on this occasion they do not.