With Britain's departure from the European Union--"Brexit"--scheduled to happen by March 29, and no replacement trade deal in sight, Britons are increasingly fearful of what a post-Brexit life might look like. An estimated 700,000 of them took to the streets of London, demanding a second vote before Brexit is finalized. Others, dubbed "Brexit preppers" are stockpiling goods, in anticipation of chaos--or at least sky-high prices--to come.

Back in 2016, British subjects voted by a narrow margin to pull out of the European Union so that their country could go its own way. The surprise victory for Brexit had several immediate consequences, including the resignation of anti-Brexit prime minister David Cameron, and the appointment of Theresa May to replace him. Though she had not supported Brexit, May promised to obey the will of the voters and pull the country out of the E.U., and on March 29, she sent a letter to the European Union, officially beginning the departure.

According to the rules of the E.U., once a member state has officially declared that it is leaving, it must complete that withdrawal within two years, which means that the U.K. has until March 29 to actually leave the E.U. The E.U. is, more than anything else, a trade partnership which means that any nation outside the E.U. will face tariffs that member states don't have to pay. May has spent the past 18 months doing her best to negotiate some sort of preferred trading status with her former European colleagues, as well as some alternative to a "hard border" between Northern Ireland (part of the U.K.) and the Republic of Ireland (part of the E.U.).

Two huge obstacles have stood in her way. First, European Union leaders have little incentive to offer the U.K. a favored trading status and every reason not to--they want to make leaving the E.U. as painful as possible so that other nations are dissuaded from trying it. And second, they have a bill to collect. According to E.U. contracts, Britain owes $39 billion pounds, or more than $50 billion, to the European Union. May has always taken the position that negotiations over that payment must happen simultaneously with negotiation of a trade agreement, so that the Europeans would only get their money if the British also got their trade deal. 

But E.U. leaders have insisted that--on the contrary--they must complete negotiations over that payment before they begin negotiations on a trade deal. For good measure, they made it illegal for any member state to negotiate its own individual deal with Britain. And that's where the two sides have been stuck for the past 18 months.

With the deadline looming, many Britons now fear that the U.K. will leave the E.U. without any trade deal, meaning it will have to pay much higher tariffs than it did before. Or that, as time runs out, May and Parliament will be forced to agree to an unfavorable trade deal. That's why the protesters want to make sure they get a second chance to vote on Brexit once they know exactly what the deal will be. They carried signs that read "Let us decide" and "Even Baldrick had a plan"--a reference to a goofy and clueless character in the long-running BBC series Blackadder. There were so many protesters that the rally set to take place in Parliament Square spilled over into surrounding streets because the crowd wouldn't fit. The London police declared themselves unable to calculate the full size of the crowd, while organizers estimated it at 700,000. A much smaller pro-Brexit rally was held nearby at the same time.

Whether this huge protest will make any difference to Brexit is not clear. With a bill enacted late last year, Parliament gave itself the right to hold a final vote on any Brexit deal before May can complete it. But since any changes to the deal would have to be renegotiated with the E.U., all Parliament can do is decide yes or no whether to go forward. May has repeatedly said that there will be no second general referendum on Brexit. On the other hand, members of parliament, especially considering the protest, might decide to vote against it in the absence of a referendum. 

Then there's the question of what would happen if either Parliament or the general electorate vote to cancel Brexit. Would the E.U. allow Britain to change its mind? Yet another unknown.

Faced with all this uncertainty, British people dubbed "Brexit preppers" are filling their cupboards and basements with extra food and medicines, enough to last several weeks, because they fear a no-deal Brexit could cause havoc at the borders and disrupt food supplies. Currently, much of what Britain consumes comes either from or through Europe. Are their fears ridiculous or reasonable? We'll have to wait and see.