After Brexit, the UK will become a third country. In the absence of a transitional agreement, its access to the EU markets will be conditioned on meeting the condition of "equivalence of regulation and supervision" as laid down in many EU regulations. Although in substance the UK regulations will be equivalent, the absence of a formal equivalence Commission decision may constitute a serious obstacle to the UK continuing to offer financial services on the EU markets. The consequences would be quite disruptive. An analysis of the different equivalence provisions reveals however a much more complex situation, indicating on the one hand that UK firms may continue to take part in the EU's financial markets through subsidiaries, on the other may offer their services to sophisticated investors, while in some cases equivalence will be in the hands not of the Commission but of the market supervisors, allowing for more flexible outcomes.