When the U.K. voted in 2016 to leave the European Union, supporters framed it as a fresh start — a win for sovereignty, the potential to save money and maintain greater control over immigration. After nearly four years of scuttled deals, missed deadlines and parliamentary shake-ups, the U.K. legally exits the EU on Jan. 31.

The U.K. government now has until Dec. 31, 2020 to renegotiate trade deals with EU member states and global partners, during which time it will remain under existing EU regulations.

While the temporary continuity gives businesses in the U.K. and EU some breathing room, they have long voiced concern about the potential for supply chain disruptions. Many have been stocking up on goods and shifting operations to mainland Europe in preparation for slowdowns at key U.K. ports and customs facilities should politicians' best-laid plans fail.

Here's a look back at how it all unfolded, and check back in the future as we chart the impact on supply chains going forward.

Brexit uncertainty: A timeline

• January 31, 2020

  Brexit becomes official

  The U.K. will withdraw from the European Union at 11pm local time on Jan. 31. It will have until Dec. 31, 2020 to renegotiate individual trade and regulatory agreements with member states before formally exiting the EU and setting out on its own.

• January 10, 2010

  Brexit vote paves way for Jan. 31 exit, future of EU trade remains uncertain

  The Brexit bill now goes to the House of Lords. If approved, the U.K.'s withdrawal from the EU could formally become law by the Jan. 31 deadline.

• October 21, 2019

  UK parliament votes to delay Brexit

  The move forces Johnson to ask the EU for an extension until Jan. 31, 2020.

• October 17, 2019

  UK and EU reach agreement on Brexit, Parliament preps for weekend vote

  The deal removed the "backstop" found in Theresa May's deal that would have kept the UK in the EU's customs union.

• April 10, 2019

  EU extends Brexit deadline to Oct. 31

  "Please do not waste this time," said European Council President Donald Tusk.

• April 3, 2019

  May agrees to meet with the opposition party

  "I am offering to sit down with the Leader of the Opposition and to try to agree on a plan — that we would both stick to — to ensure that we leave the European Union and that we do so with a deal," May said.

• April 1, 2019

  Parliament votes on four indicative votes, none gains a majority

  The customs union was the closest to gaining a majority, but still failed 276-273.

• March 28, 2019

  Parliament votes on eight indicative votes, none gains a majority

  The votes came after Prime Minister Theresa May said she planned to step down if her Brexit agreement is passed and the U.K. leaves the EU.

• March 25, 2019

  Parliament takes control of Brexit away from May, plans indicative votes

  "I must confess that I am skeptical about such a process of indicative votes," May told Parliament before the vote to shift control passed.

• March 21, 2019

  EU agrees to Brexit deadline extension

  The EU agreed to move the deadline to May 22 if Prime Minister Theresa May could persuade Parliament to pass her withdrawal agreement.

• March 18, 2019

  Brexit plan must change 'substantially' for vote

  The speaker of the House of Commons in the British Parliament, John Bercow, said Prime Minister Theresa May cannot bring her Brexit legislation up for a vote unless it is "substantially" different than the previous versions that failed.

• March 14, 2019

  Parliament votes in favor of three month Brexit extension

  This still had to be brought to the EU for approval.

• March 12, 2019

  Brexit agreement fails again, UK publishes 'no-deal' guidance

  Parliament rejected Prime Minister Theresa May's Brexit proposal for the second time with a vote of 391 to 242.

• March 6, 2019

  Automakers warn of no-deal Brexit

  Toyota and BMW said this scenario could make U.K. business untenable.

• Feb. 27, 2019

  Boeing shuffles supplies ahead of Brexit

  Boeing began shifting spare airplane parts around its distribution centers in the U.K. and around the world in preparation for a potential no-deal Brexit.

• Feb. 22, 2019

  Retailers warn of Brexit-induced tariff hikes

  The British Retail Consortium said a no-deal Brexit could result in tariff hikes of up to 45% on "some everyday food items."

• Feb. 5, 2019

  Honda to close 34-year-old UK plant

  Honda plans to close its plant in Swindon, England, at the end of its current production cycle, which ends in 2021.

• Feb. 4, 2019

  UK offers simplified customs in case of 'no-deal' Brexit

  The government sent letters to 145,000 businesses currently doing business with the EU to let them know about the new rules and what they need to do to prepare.

• Jan. 23, 2019

  Amazon, DHL prepare for a hard Brexit

  Amazon advised its U.K.-based sellers to build up inventory and prepare for a slowdown or shutdown of cross-border shipping in the event of a hard Brexit.

• Jan. 3, 2019

  UK preps emergency supply chain

  The U.K. awarded three freight contracts worth 108 million British pounds ($135.9 million) to help ease congestion on the English Channel.

• Oct. 31, 2018

  Air transport association sounds alarm on Brexit impact

  The International Air Transport Association warned Brexit — "hard" or not — could pose significant risks to air-reliant supply chains in the U.K.

• Oct. 24, 2018

  Aston Martin eyes supply chain shifts as Brexit nears

  The British automaker currently brings in several parts from the Port of Dover, which is just 25 miles from the Port of Calais in France.

• July 9, 2018

  British retailers warn of no-deal impact on food supply chains

  The British Retail Consortium estimated 12,500 small businesses would face a high risk of folding if negotiators don't reach a deal.

• July 5, 2018

  Port of Rotterdam plans to test post-Brexit customs

  Port of Rotterdam Authority CEO Allard Castelein said he feared the port could lose half of its throughput from the U.K. if Brexit negotiations result in "no deal" between the two parties.

• March 12, 2018

  EU ports warn of ocean freight bottlenecks post-Brexit

  The European Sea Ports Organization called on Brexit negotiators to make maritime transport and the flow of goods between ports a priority in their talks.

• Nov. 7, 2017

  UK buyers, suppliers face the costs of Brexit

  The number of non-British European companies expecting to relocate at least part of their supply chains out of the U.K. rose to 63% from 44% when surveyed in May.

• June 24, 2016

  U.K. votes to leave the European Union in referendum

  The decision led the pound to plummet as "leave" supporters celebrated, The Guardian reported.