How to watch the UK election like a pro

LONDON — British voters will go to the polls again on December 12, to vote in the country’s third general election in five years.

Here’s POLITICO’s guide to what many say will be the most significant U.K. election in a generation.

Why is this election happening?

When Boris Johnson succeeded Theresa May as prime minister in July, he knew he would have to face the electorate soon.

Within days of taking office, his working majority in parliament was reduced to one as the Conservatives lost a by-election in Brecon and Radnorshire. He later lost it altogether when he expelled 21 of his MPs (though he later allowed 10 to rejoin).

The lack of a parliamentary majority prevented both May and Johnson from passing their Brexit deals through parliament. Johnson had been fruitlessly pressing for a snap poll for weeks, but on October 29 opposition parties backed a bill to trigger the national ballot on December 12.

It will be the first U.K. general election held in December since 1923.

How many seats are being contested?

There are 650 parliamentary constituencies in the U.K., each of which is represented by an MP. They are all up for election.

The vast majority of seats — 533 — are in England,

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