Britain will go to the polls on December 12 after the House of Commons voted in favour of Prime Minister Boris Johnson's bid to break the Brexit deadlock.

Key points: Boris Johnson has succeeded in gaining support for a December election

Boris Johnson has succeeded in gaining support for a December election Ten of the 21 Tories expelled from the party last month have been readmitted

Ten of the 21 Tories expelled from the party last month have been readmitted Opposition Leader Jeremy Corbyn says Labour is ready to win election

In the third and final reading of the election vote before the bill goes to the House of Lords, British MPs voted in favour of Britain's first December election in almost a century, 438-20.

It will become law once it is approved by the unelected House of Lords, which does not have the power to overrule the elected Commons.

"It's time to unite the country and get Brexit done," Mr Johnson said following the House of Commons vote.

As the European Union granted a third delay to the divorce that was originally supposed to take place on March 29, the United Kingdom, its Parliament and its voters remain divided on how or indeed whether to go ahead with Brexit.

Mr Johnson, who had promised to deliver Brexit on October 31 "do or die", had repeatedly demanded an election to end what he casts as a nightmare paralysis that is sapping public trust by preventing any Brexit outcome at all.

After Parliament refused Mr Johnson his third demand for an election on Monday (local time), he managed to force a bill through Parliament on Tuesday with the support of Opposition Leader Jeremy Corbyn.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 20 seconds 20 s UK Labour leader supports December election

An earlier Labour amendment, which would have changed the election date to December 9, was voted down 315-295.

Mr Johnson needed a simple majority in Parliament, but in September, he lost his working majority in the House of Commons, which has stymied the Government's legislative agenda.

In a move that resulted in a rare parliamentary success for Mr Johnson, Mr Corbyn, who heads the opposition Labour Party, said its condition of ruling out a no-deal Brexit had been met so it supported an election.

"Whatever date the House decides the election will be, I'm ready for it, we're ready for it," Mr Corbyn told Parliament, adding that he supported allowing EU citizens with settled status and 16–17-year-olds to vote.

That was a step too far for the British Government, which said it would pull the election bill if the House voted to include these newer voters, because they claim it would result in a six-month delay.

According to the Leader of the House of Commons, Jacob Rees-Mogg, the dissolution date for Parliament is next Wednesday, November 6.

Johnson readmits 10 MPs

Mr Johnson has readmitted 10 of the 21 Conservative MPs he expelled from his parliamentary party last month, a spokesman for the governing party said on Tuesday.

The spokesman said Mr Johnson met the 10 in his office in Britain's House of Commons. Among their number was former business minister Greg Clark and Nicholas Soames, grandson of British wartime leader Winston Churchill.

Some of them have already said they will stand down at the next election.

"The expectation of all Tory (Conservative) MPs and candidates standing for an election will be that when we come back, we get this (Brexit) deal passed," the spokesman said.

The first Christmas election in Britain since 1923 will be highly unpredictable: Brexit has variously fatigued and enraged swathes of voters while eroding traditional loyalties to the two major parties, Conservative and Labour.

Some politicians feel an election so close to Christmas could irritate voters, while campaigning and getting the vote out could be hampered by cold winter weather and darkness setting in by mid-afternoon.

'The most unpredictable election I've ever known'

Mr Johnson does not govern with a working majority in the House of Commons. ( Reuters: UK Parliament/Roger Harris )

Mr Johnson said the House of Commons was obstructing Brexit and thus damaging the economy by preventing investment decisions, and corroding faith in democracy.

"There is only one way to get Brexit done in the face of this unrelenting parliamentary obstructionism — this endless wilful fingers-crossed 'not me Guv' refusal to deliver on the mandate of the people — and that is, Mr Speaker, to refresh this Parliament and give the people a choice," Mr Johnson said.

Meanwhile, the legislation enacting Mr Johnson's Brexit deal has been put on hold, pending an election, Jacob Rees-Mogg, who oversees the Government's legislative agenda in the House of Commons, said.

While almost all British politicians agree that an election is needed, Mr Johnson's opponents want to inflict maximum political damage by preventing his last-minute deal from being ratified before the poll.

Mr Johnson, in turn, is trying to shift the blame for failing to deliver Brexit by October 31 on to Parliament.

"This House cannot any longer keep this country hostage," Mr Johnson said.

But if no party wins conclusively, the Brexit deadlock would continue.

Mr Johnson's Conservatives are ahead of Labour by an average of about 10 percentage points in polls this month, though British pollsters have been viewed with cynicism in recent years given their failure to predict the Brexit referendum's outcome.

Britain's Liberal Democrat leader Jo Swinson, centre, is poised to corral pro-Remain voters. ( House of Commons via AP: Stephen Pike )

Both major parties face a fight on at least three fronts: the hardline Brexit Party led by Nigel Farage will seek to poach Brexit voters while the Liberal Democrats will seek to win over opponents of Brexit.

"This will probably be the most unpredictable election I have ever known," Anand Menon, director of The UK in a Changing Europe, told Reuters.

"Is it Brexit or is it not? We don't know. Second, the election is as volatile as ever and, thirdly, the potential for tactical voting — and tactical voting to go wrong — is very high given the Leave-Remain split," he said.

ABC/wires