Brexit Showdown Looms as UK Threatens to Undermine Divorce Treaty

The flag of the European Union and the British national flags are flown on poles during a demonstration outside the Palace of Westminster in London on Feb. 27, 2019. Alastair Grant/AP Photo

LONDON—Brexit trade talks plunged into crisis on Monday after Britain warned the European Union that it could effectively override the divorce deal it signed unless the bloc agrees to a free trade deal by Oct. 15.

In one of the most startling turns of the four-year Brexit saga, Britain is reportedly planning new legislation that will override key parts of the Brexit Withdrawal Agreement—a step that, if implemented, could jeopardise a treaty signed in January and stoke tension in Northern Ireland.