It was in June 2016 when 52 per cent of U.K. voters chose to leave the European Union. More than three years later, they remain, with a divorce deal yet to be agreed on, while the issue has become a political morass.

So far, Brexit has led to the resignation of Theresa May as prime minister, the installation of Boris Johnson as party leader to take her place, and warnings that the U.K. may be facing a constitutional crisis.

Johnson has vowed to complete the departure from the EU by Oct. 31, with or without a deal (also known as a "no-deal" Brexit).

But he suffered a significant defeat in the House of Commons when members of his own party joined opposition members to support a bill to prevent a no-deal Brexit. He also suffered a key defection when Conservative MP Phillip Lee crossed the floor of the House of Commons to join the pro-EU Liberal Democrats, costing Johnson his working majority in Parliament.

Then Parliament rejected his motion to call an early election.

So what does all this mean for Brexit? Will Britain actually leave the EU on Oct. 31? What does "no-deal" mean? And what happens next? Here are the answers to some of the big questions.

Wasn't Brexit supposed to have happened already?

Yes. Brexit had been scheduled to happen on March 29, two years after then-prime minister Theresa May triggered the Lisbon Treaty's Article 50, the mechanism by which a member state leaves the bloc. But the deadline was delayed, in part because the British Parliament three times rejected a withdrawal deal agreed between the May government and the EU.

In April, the EU and May agreed to delay Brexit until Oct. 31.

What's a no-deal Brexit?

A no-deal Brexit simply means that the U.K. would leave the EU on Oct. 31 without having agreed on the terms of its divorce, which includes issues like how much money the U.K. would pay the EU, how trade would work, and what rights EU citizens would have in the U.K. (and vice-versa). Johnson has threatened to leave without a deal, but a spokesperson for the PM said they "absolutely want to do so with a deal."

Analysts at the Dutch-based ING Group, a financial services corporation, created a Brexit possibility flow chart, including predictions on which Brexit scenario is most likely. (ING)

Opposition parties including the Labour Party, the Liberal Democrats, the Scottish Nationalist Party and even some so-called rebel Conservatives all oppose Britain leaving the EU without hammering out a deal with the bloc beforehand.

Can Parliament stop a no-deal Brexit?

The opposition, along with some Conservatives, want to extend EU membership beyond the Oct. 31 deadline to try and negotiate a new withdrawal deal. A bill to extend the deadline to Jan. 31, 2020, was approved by the House of Commons on Wednesday and proceeded to the House of Lords, which agreed it will let the bill pass on Friday. This means it could be law on Monday.

However, the new deadline would still have to be approved by the other 27 member states of the EU. Johnson has said he would rather be "dead in a ditch" than ask the EU to delay Brexit. But he also refused to say whether or not he would resign if forced to ask for another delay.

So why is Johnson trying to call an election?

Johnson had said if legislation passes that thwarts his attempts to push ahead with Brexit, he would bring his own motion calling for a general election, hoping to win a stronger majority and thus push Brexit through on Oct. 31.

His first attempt was unsuccessful. On Wednesday, Johnson asked Parliament to back an Oct. 15 election, but Parliament said no. He needed the support of two-thirds of the 650 lawmakers in the House of Commons — a total of 434 — but got only 298, with 56 voting against and the rest abstaining.

But with the expectation that the no-deal-blocking legislation will get royal assent on Monday, Johnson is expected to bring another motion calling for an election that evening, said Ruth Fox, director of the British-based Hansard Society.

"So he's banking on the fact that the opposition will feel uncomfortable to deny him an election at that point." Fox said.

What about a no-confidence motion?

Lee's decision to cross the floor and join the Liberal Democrats took away Johnson's working majority of one. But in order for the government to fall, the opposition would have to introduce a no-confidence motion.

Labour Leader Jeremy Corbyn had called on other opposition party leaders and MPs to support him if he were to table a vote of no confidence in Johnson's government. If the Johnson government did topple, Corbyn would make a play for prime minister, as the leader of the second biggest party.

However, the Liberal Democrats and some Tory MPs said they would not support any plan that saw Corbyn become prime minister — even on a temporary basis, the BBC reported. And some of Corbyn's own MPs oppose the move, arguing Parliament's focus should be on forcing the prime minister to seek a new Brexit deal, the Financial Times reported.

Losing a confidence vote triggers a 14-day period in which other lawmakers can try to get the backing to form a new administration. If that doesn't happen, there will be a general election.

But the electoral legislation allowing for this was introduced in the fixed-term Parliaments Act of 2011 and has never been tested in this way. It has been criticized for not defining exactly how the 14-day period would work and who has the power to do what during it.

Could Johnson seek a no-confidence motion against his own government?

Theoretically, yes. It was certainly not the intention of the fixed-term Parliaments Act that the governing party should be able to lay a motion of no confidence in itself, Fox says.

"However, the law doesn't say you can't. It's silent on that," Fox said. "So it's entirely possible that they could come forward with a motion: this House has no confidence in Her Majesty's government."

What's the main sticking point in agreeing to a Brexit deal?

The outstanding issue that has been the most difficult to resolve is the so-called Irish border backstop. It's considered the main reason the British Parliament repeatedly rejected the deal May negotiated with the EU. Johnson opposes the backstop provisions in his predecessor's deal. He has told European Commission President Jean-Claude Juncker that there was no prospect of a Brexit deal unless the Irish border backstop was abolished.

The backstop provision in the proposed withdrawal agreement by May, and approved of by the EU, is aimed at keeping an open border between EU member Ireland and British-ruled Northern Ireland. It would prevent the return of a physical border and border controls between the two.

Right now, people and goods flow freely between the Republic of Ireland and Northern Ireland, with no need for customs checks. Brexit could change all that.

But critics of the backstop argue that it would keep the U.K. bound to EU customs regulations, which would derail Britain's efforts to strike other international trade deals.