The U.K. Has Finally Cut Ties With the EU. Here’s What Has Changed.

The U.K. left the European Union behind Thursday, 48 years after it joined the bloc, a significant shift in the global order that will also bring big changes for ordinary Britons.

On Jan. 1, decades of trade with the EU unencumbered by customs declarations and regulatory obstacles ceased, one of several changes likely to have big and lasting effects on the British economy. The rights of a U.K. citizen to live, work or study in any other EU member state also fell away, highlighting the extent of the EU’s reach into its citizens’ daily lives. EU citizens also lost those rights in the U.K.

For supporters of Brexit, including Prime Minister Boris Johnson, such costs are justified by the benefits and opportunities that exiting the EU will bring. Leaving will allow the U.K. to boost British trade with the rest of the world and set laws to shape its economy and society without interference from Brussels, they say.

“Brexit is not an end but a beginning and the responsibility now rests with all of us to make the best use of the powers that we have regained,” Mr. Johnson said Wednesday during a debate on the U.K.-EU free-trade agreement in Parliament.

The agreement reached on Christmas Eve between London and Brussels on the terms of their future relationship ran to more than 1,000 pages, covering areas as diverse as fishing rights and cooperation between law-enforcement agencies.