UPDATE 1-FTSE 100 ends flat on US tariff uncertainty

​The UK's FTSE 100 ended flat on Monday as uncertainty over U.S. trade policy largely stymied trade, although Johnson Matthey slumped ‌after the chemical company accepted a cut to the sale price of its catalyst unit to Honeywell.

The blue-chip index ended 0.02% lower after closing at record highs last week. The domestically focused mid-cap FTSE 250 ‌was down 0.9%. U.S. President Donald Trump at the weekend said he would implement a new ‌15% tariff on global imports, following the U.S. Supreme Court's decision on Friday to strike down his emergency-based tariffs. The British government had negotiated a lower reciprocal tariff rate at 10% after reaching a deal with the U.S. last year, ⁠but Trump's ​promise to reimpose ⁠higher levies at 15% means businesses may face higher duties.

MONDI AND JOHNSON MATTHEY BOTH FALL Britain does not expect the ⁠new tariffs to impact the "majority" of a UK-U.S. economic deal, Prime Minister Keir Starmer's spokesperson said. Tariff concerns weighed ​on packaging and paper group Mondi , which lost 4.3%, while its U.S. peers also ⁠fell. Johnson Matthey slumped 16.4% to the bottom of the mid-cap index, after it agreed to lower the sale price ⁠of ​its catalyst technologies business to Honeywell following the unit's underperformance in fiscal 2025. British aerospace and defence stocks pulled back after touching a record high on Friday. Rolls-Royce Holdings dipped 0.2% despite a ⁠media report that said the engine maker is expected to launch a share buyback worth as much ⁠as 1.5 billion ⁠pounds ($2 billion) alongside its annual results this week.

Meanwhile, precious-metal miners rose 5.2% to a record high after gold climbed to a three-week high as investors ‌sought safe-haven assets.