President Trump abruptly raised global tariffs from 10% to 15% just 24 hours after implementing them, undermining a key trade deal with the United Kingdom. The move came after the Supreme Court struck down his previous tariffs under the International Emergency Economic Powers Act, forcing him to impose new duties under Section 122 of the 1974 Trade Act.

The 15% rate must be applied uniformly to all trading partners, contradicting the Trump administration's separate agreement with Britain that had secured a preferential 10% rate. British Prime Minister Keir Starmer had taken a conciliatory approach to Trump's previous tariffs, with administration officials touting the UK deal as a model for favorable treatment. The tariff hike effectively nullifies that arrangement.

While the headline rate increased by 5 percentage points, analysts note the effective tariff rate will only rise about 2 points to 14.5% due to existing exemptions. The administration is simultaneously pursuing investigations under Section 301 and 232 of trade laws that could lead to additional targeted tariffs. JPMorgan analysts predict the average tariff rate will eventually settle around 9-10%, but warn that trade uncertainty will remain elevated