LONDON – Another day of high political drama was expected in Britain on Wednesday as Prime Minister Boris Johnson faced a potential fight to call a general election after rebel lawmakers took a decisive step toward taking control of the Brexit process.

The battle over Britain's efforts to leave the European Union intensified Tuesday as opposition and rebel lawmakers from Johnson's ruling Conservative Party effectively began wresting control of Brexit from him on a day when Britain's leader suffered key defections and was deprived of his parliamentary majority.

In a vote, parliamentarians successfully challenged Johnson’s insistence that the nation will leave the E.U. on Oct. 31 with or without a formal withdrawal agreement.

Lawmakers tentatively approved proposed legislation that would force Johnson to request that the E.U. delay Brexit until Jan. 31 unless a new exit deal is approved by the Halloween deadline – or unless Parliament votes in favor of a "no-deal" Brexit.

The outcome, which needs to be confirmed in a series of further votes on Wednesday and later this week, means that Johnson likely won't be permitted to take Britain out of the E.U. without an exit deal. It also means Johnson will try to call a general election, deepening Britain's political crisis three years after it voted to leave the political bloc.

Johnson lost the vote 328 to 301, with a total of 21 lawmakers, including several ex-cabinet members, siding with opposition parties to defeat Johnson's government. Among the rebels was Sir Nicholas Soames, Winston Churchill's grandson.

"Let there be no doubt about the consequences of this vote tonight," Johnson said in Parliament, visibly annoyed at the result. "Parliament is on the brink of wrecking any deal we might reach with Brussels. This will mean more dither and more delay."

Johnson said his only remaining option was to call an October election.

"The people of this country will have to choose," he said.

More:Britain's Prime Minister Boris Johnson is like Trump. Only he isn't.

If an election takes place, it will be Britain's third general election in four years. A general election can only be called every five years unless a prime minister gets approval from two-thirds of lawmakers. Johnson can choose the vote's date. It's not immediately clear if he will be able to achieve the sufficient parliamentary math for that.

Oct. 15. has been suggested as one possible date for the vote.

The situation remains fluid and subject to change but lawmakers may vote on whether to have a new election around 8:30 p.m. local time (3:30 p.m. EST).

Ahead of Tuesday's vote, Johnson's ruling Conservative Party lost its slim working parliamentary majority of just one seat after a Conservative Party politician, Philip Lee, defected to the Liberal Democrats, saying he left because "this Conservative government is aggressively pursuing a damaging Brexit."

Brexit files:Boris Johnson asks Queen Elizabeth to suspend Parliament

Economists believe a "no-deal" Brexit is a potentially dangerous move because it will overnight do away with decades of seamless trade and cooperation of the E.U. bloc's single market of 500 million people. It could lead to disruption of travel and supplies and lead to a "hard" border between E.U. member Ireland and Northern Ireland, which is part of the United Kingdom. Johnson is adamant that the potential for leaving without a deal must remain as a bargaining chip in E.U. negotiations, but the E.U. has repeatedly made it clear that it is not willing to renegotiate the agreement struck with former Prime Minister Theresa May, which led to her downfall.

"Leaving without a deal will have significant negative consequences for the U.K. economy. Nor will it mark the end of Brexit, merely herald in the start of negotiations that promise to be significantly more difficult than those we have witnessed to date," said Anand Menon, a professor of politics at King's College London and the author of a report published Tuesday by think tank The UK in a Changing Europe.

Johnson's decision to attempt to hold any new vote two weeks ahead of Britain's official Brexit date has led analysts and political commentators to speculate that it may be a move designed to shore up "no-deal" support from his own Conservative Party.

"We are finding ourselves in the middle of a full-throttle confrontation between a Parliament that does not want to allow the country to leave the EU without a deal and a prime minister who secured his place in power promising he would always keep that option," wrote Laura Kuenssberg, the BBC's chief political commentator, in a blog post.

Sir Keir Starmer, Brexit Secretary for the main opposition Labour Party, told BBC radio Wednesday that his party was in favor of an election, but that he did not "trust" Johnson to hold the election before the Brexit deadline. "We are not shy of a general election but we are not going to be trapped into abandoning control of Parliament or be taken in what Boris Johnson says because we don't trust him," he said.

The prime minister has already controversially shortened the time lawmakers have to debate Brexit by suspending Parliament for five weeks from the start of next week. He has also threatened to ban from standing at the next election any Conservative Party politicians who voted with the rebels to prevent a "no-deal" Brexit.

Traveling with pets in Europe:No-deal Brexit would make crossing borders much tougher

Ahead of the vote on Tuesday, Jeremy Corbyn, leader of the Labour Party, accused Johnson of "riding roughshod" over the constitution in order to crash Britain out of the EU without a deal.

"He isn’t winning friends in Europe. He’s losing friends at home. His is a government with no mandate, no morals and, as of today, no majority," Corbyn said.

As Brexit has faced delays, international investors have showed concern.

The British pound fell as low as $1.1960 on Tuesday, down a cent on the day before, before stabilizing around $1.1990, where it remains Wednesday near historic lows.

Confused about Brexit? Here's a brief primer

June 2016: British public vote to leave the European Union. "Leave" side wins by a narrow majority.

March 2017: British government formally triggers Article 50, legislation backed by Parliament that gives the E.U. notice it will leave the bloc in two years.

November 2018: British Parliament and E.U. leaders agree to tentative withdrawal agreement over the objection of many British lawmakers who worry about how the deal treats the status of the free-trade border between E.U.-member Ireland and North Ireland (part of the United Kingdom) after Brexit.

November 2018-March 2019: British Prime Minister Theresa May fails three times over several months to get parliamentary approval for deal agreed with E.U.

March 29: Initial Brexit deadline passes. May requests new June 30 deadline. The E.U. grants a longer extension, until Oct. 31.

May 24: After months of pressure, May announces she will resign as prime minister effective June 7, but will stay on in a caretaker capacity until a successor is found.

May 23-26: Britain participates in E.U. parliamentary elections even though it is still expecting to leave the E.U.

July 24: Boris Johnson is appointed prime minister after an internal Conservative Party vote. In Britain, a party, not a specific leader is elected. Johnson vows to deliver Brexit with or without a formal withdrawal agreement with the E.U.

Aug. 28: Johnson asks Queen Elizabeth to "prorogue" or suspend Parliament from Sept. 10, boosting his chances of delivering Brexit with or without an E.U. exit deal.

Sept. 3: Parliament to return from recess. Lawmakers tentatively approve proposed legislation aimed at preventing a "no-deal" Brexit.

Sept. 10: Parliament expected to be "prorogued" or suspended per Johnson's request.

Oct 14: Potential British election.

Oct. 17-18: Last scheduled E.U. summit where Brexit will be discussed.

Oct. 31: Britain expected to formally leave the E.U.