However, under the EU deal, 15% is the maximum tariff, and isn't added to any existing rate. For Britain, the 10% base rate is in addition to the "most-favoured nation" (MFN) rates that the U.S. applies as a minimum to specific goods imports from all its trade partners, so the effective tariff rate is often higher.

The deal, that includes a 15% tariff on EU goods entering the U.S. and significant EU purchases of U.S. energy and military equipment, will bring