The UK officially left the European Union on January 31, 2020 and the country has implemented new rules for goods and services to be imported into the UK.  Starting on January 1, 2021, all UK imports and exports will fall under the World Trade Organization (WTO) terms, which requires changes to many fulfillment processes for U.S. e-commerce parcel deliveries to the UK.

More info : https://blog.stamps.com/2020/12/22/shipping-from-t...