Factbox: How will Britain's Dec. 12 'Brexit election' work?

LONDON (Reuters) - Britain will hold a general election on Dec. 12, electing 650 new members of parliament, from which a government will be formed. Their first task will likely be to decide how, when and if the country will leave the European Union.

Below are the key facts about how the election will work:

WHAT ARE PEOPLE VOTING FOR?

- The country is divided into 650 regions, known as constituencies.

- Each constituency equates to one seat in parliament's House of Commons. There are:

533 in England

59 in Scotland

40 in Wales

18 in Northern Ireland

- In each constituency, voters vote for a local candidate.

- Candidates represent a political party, or are independent.

- The candidate who receives the most votes wins the seat.

- Voting takes place on Dec. 12 from 0700 GMT until 2200 GMT.

- Votes can be cast in person at polling stations across the country, or in advance by post.

WHO CAN VOTE?

- There are 45.8 million registered voters in England, Wales, Scotland and Northern Ireland.(1)

- British citizens resident in the country and aged 18 years or over on Dec. 12 are eligible to vote.

- Irish and some Commonwealth citizens resident in the country can also vote. Britons living overseas can also vote if they have registered to vote in Britain during the previous 15 years.

WHEN ARE THE RESULTS ANNOUNCED?

- An exit poll published at 2200 GMT usually gives a good idea of how the election has gone. In three of the last four elections, this poll has correctly called the overall result, albeit with a margin of error on actual numbers of seats.

- Most constituencies begin counting votes immediately after the polls close at 2200 GMT.

- The first results are usually available within a few hours, and the bulk are expected in the early hours of Dec. 13.

- All results should be declared by the end of Dec. 13.

WHAT HAPPENS NEXT?

- If there is a clear winner or loser based on the exit poll and the subsequent declaration of actual results, an opposition leader may choose to concede, or a winner may declare victory.

- If the result is expected to be close, parties are likely to wait until almost all the results are in.

HOW MANY SEATS TO WIN?

- An absolute majority in parliament is 326 seats.

- However, the actual number for a working majority is lower. This is because lawmakers elected for the Sinn Fein party in Northern Ireland do not take up their seats.

- For example, at the 2017 election Sinn Fein won seven seats, effectively lowering the threshold at that election to 322.

WHAT IF THERE IS NO CLEAR WINNER?

- If no party wins a majority, it is called a 'hung parliament'.

- If this happens, parties can try to form an alliance with one another to give them enough support to win a vote in parliament.

- The incumbent - in this case Prime Minister Boris Johnson - would get first try at putting together an arrangement to command a majority in parliament.

- This could be under a formal coalition arrangement, as happened in 2010 between the Conservatives and the Liberal Democrats.

- It could also be a 'Confidence and Supply' agreement with a smaller party to support the government, as happened in 2017 between the Conservatives and the Democratic Unionist Party.

- If Johnson cannot form a government he can resign and recommend that the leader of the largest opposition party is given a chance to form the executive.

(1) According to the latest available data from the Office for National Statistics, which was collected in December 2018 and released in March.

(Reporting by William James; editing by Guy Faulconbridge and Toby Chopra)