The European Union on Thursday launched legal action against the United Kingdom over London’s plan to unilaterally breach a Brexit withdrawal agreement both sides signed last year. In the latest setback in Britain’s attempt to separate itself from the E.U., the European Commission said in a statement that the country had been put on “formal notice” for tabling its own law that by British ministers’ admission breaches international law. The statement said the U.K.’s controversial Internal Market Bill would “flagrantly violate” the rules governing the border between the Irish Republic and Northern Ireland — a key stumbling block in Brexit talks for the last four years.