Though the United Kingdom formally left the European Union on 31 January 2020, the departure was only substantively completed eleven months later when the transition period ended on 31 December 2020. The departure does not negate, however, the need for collective action at a supranational level to tackle supranational problems, as underscored by the UK’s implementation of the Anti-Tax Avoidance Directive. This article teases out various aspects of the UK’s implementation of the Directive.