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 European Union is facing a higher 15% tariff rate on its goods imported to the U.S. compared to the 10% levy the U.K. has agreed to. "In theory, the UK benefits," Philip Shaw, chief economist at Investec, told CNBC.

Donald Trump has struck an agreement with the European Union to reduce tariffs - what will that mean for the UK?