* Johnson: End this Brexit 'obstructionism'
* Labour's Corbyn says he supports election
* EU's Tusk: This Brexit delay may be the last
* Proposals to extend franchise not selected (Adds demands to lower voting age will not be included)
LONDON, Oct 29 (Reuters) - Britain was heading towards its first December election in almost a century after Prime Minister Boris Johnson's bet on breaking the Brexit deadlock with an early ballot gained support from opposition parties on Tuesday.
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 electorate remain divided on how or indeed whether to go ahead with Brexit.
Johnson, who had promised to deliver Brexit on Oct. 31 "do or die", has repeatedly demanded an election to end what he casts as a nightmare paralysis that is sapping public trust in politicians by frustrating any Brexit outcome at all.
After parliament refused Johnson his third demand for an election on Monday, he will try to force a bill through parliament on Tuesday that calls for a Dec. 12 election. It needs a simple majority in parliament.
In a move that aligns the stars for an election after months of Brexit discord, Jeremy Corbyn, leader of the main opposition Labour Party, said he would back an election now the threat of Britain leaving the EU without a deal had been removed.
"Whatever date the House decides the election will be, I'm ready for it, we're ready for it," Corbyn told parliament.
A last-minute row over expanding the electoral franchise that could have sunk Johnson's election bid was averted when opposition proposals to grant the vote to EU citizens with settled status and 16-17 year olds were not included in a provisional list of amendements to be voted on.
The first Christmas election in Britain since 1923 would 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.
Ultimately, voters would have a choice between an emboldened Johnson pushing for his Brexit deal or a socialist government under Corbyn renegotiating the deal before another referendum.
If no party wins conclusively, the Brexit deadlock would continue.
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," Johnson said.
After four years of arguing over Brexit, almost all British politicians now agree an election is needed to break the cycle of inaction that has shocked allies of a country once considered a bastion of stable Western capitalism and democracy.
An election, though, could decide the fate of Brexit as well as the main players - PM Johnson, 55, and his rival Corbyn, 70.
When Johnson's predecessor, Theresa May, bet on an early election in 2017, she lost her slender majority - a failure that ultimately prevented her from ratifying her Brexit deal in parliament and sank her political career.
Johnson's Conservatives are ahead of Labour by an average of about 10 percentage points in polls this month, though pollsters underestimated the support for Brexit in 2016 and admit that the models they use are wilting beside the Brexit furnace.
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.
VOTES ON VOTES
Lawmakers on Tuesday approved the timetable for Johnson's "Early Parliamentary General Election Bill" without a formal vote. Two votes on the bill itself will take place from about 1730 GMT.
Lawmakers could still bring significant amendments to Johnson's bill. Opposition parties are squabbling over which day in early December is best for an election.
The House of Commons will not vote on opposition proposals allowing EU citizens to take part in parliamentary elections or lowering the voting age to 16, according to an official document showing the provisional selection of amendments.
Johnson had warned he would cancel plans to hold a snap election if parliament voted for such changes.
As Johnson moved closer to an election than he has ever been in his tumultuous three-month premiership, the EU granted a Brexit delay to Jan. 31 but warned it might be the last.
"The EU27 has formally adopted the extension. It may be the last one. Please make the best use of this time," outgoing European Union chairman, Donald Tusk, said on Twitter.
Among voters, there was some relief that the Brexit debate might be ending soon.
"We've just got to bring this to some sort of resolution," commuter Matt Finch, 36, said outside London's Charing Cross rail station on Tuesday. "We've had many votes in the last 12 months in parliament and I think a general election might be a way to sort it all out."
(Additional reporting by Kylie MacLellan, Paul Sandle, Helena Williams, Andrew MacAskill and Kate Holton in London and Gabriela Baczynska in Brussels; Writing by Guy Faulconbridge; Editing by Janet Lawrence, Mark Heinrich and David Clarke)