2020年12月24日歐盟與英國終於完成英國脫歐後的雙邊未來關係協議談判，簽署了貿易暨合作協定，歐洲議會於2021年4月27日完成同意程序，自2021年5月1日起生效，也讓歐盟與英國未來的關係有了新的法律基礎。歐盟競爭法立法宗旨爲促進在歐洲單一市場內的競爭維持及保障競爭自由、規範企業的違法競爭行爲，以確保企業不會成立卡特爾或壟斷市場進而損害社會利益。由於歐盟對於單一市場的競爭政策享有專屬職權，而歐盟的競爭法不僅適用於全體會員國，更是擴及歐洲經濟區的成員，同時歐盟法院肯認歐盟競爭法具有域外效力，因而英國退出歐盟後，英國即不再適用歐盟的競爭法而是自己的競爭法，對於第三國企業而言，歐盟與英國競爭法為兩套法律，歐盟執委會與英國的競爭暨市場局分別負責競爭調查事宜。英國脫歐後，歐盟與英國競爭法的適用與這兩套競爭法之關係，均有釐清之必要。
The EU and the UK finally completed the negotiation of the bilateral agreement for the future relationship after Brexit and signed the EU - UK Trade and Cooperation Agreement on December 24, 2020. This comprehensive Agreement was temporarily enacted since January 1, 2021. The EU - UK Trade and Cooperation Agreement temporarily became the new legal framework for the future relationship between EU and UK. The EU competition law aims to promote maintaining competition and guarantees free competition within the Single Market. The EU competition law ensures undertakings by cartel or abusive market domination from causing damages to the public interest. The EU has an exclusive power over the competition policy for the Single Market. The EU competition law applies not only to all member states, but also to members of the European Economic Area. The Court of Justice of the EU has confirmed the extraterritorial effects of the EU law. The EU competition law is no longer applicable in the UK after Brexit. The UK has its own competition law. Therefore, the EU competition and UK's competition law are two legal systems for undertakings from third countries after Brexit. The One-Stop-Shop principle is no longer applicable after Brexit. Undertakings from third countries face two investigations against anti - competitive behaviors by the European Commission and the UK's Competition and Market Authority. The impact of Brexit is legally uncertain for undertakings. The costs of legal consultation are to be considered for undertakings. It might hinder multinational undertakings from investing in the UK. On the other hand, the UK's Competition and Market Authority confronts a huge challenge of the manpower deployment. The UK also withdraws the European Competition Network after Brexit. It has blocked the exchange of information on competition issues between the European Commission and the UK's Competition and Market Authority. Indeed, this is a bad phenomenon for both parties. It is necessary to learn the application and the relationship between the European and British competition law after Brexit.
