Two of the world’s biggest tobacco companies have filed lawsuits challenging the U.K. government over its plans to ban branding on cigarette packs. Philip Morris International Inc. and British American Tobacco PLC filed separate suits with the High Court in London on Friday. Both companies claimed the “plain packaging” law—which will come into effect next year—violates U.K. and European law....Imperial Tobacco Group PLC and Japan Tobacco International Inc.—which together control around 85% of sales in the U.K.—have previously said they would take legal action, although lawsuits are yet to be filed.