jats:titleAbstract</jats:title>jats:pWith the United Kingdom having finally withdrawn from the European Union, and with a new Trade and Cooperation Agreement in place to begin to manage their economic relationship, it might be thought that the constitutional drama of ‘Brexit’ was finally at an end. Yet the longer‐term constitutional implications of Brexit and its repatriation of the European regulatory state are becoming apparent. This is particularly evident in the decision of the UK Government to legislate for a United Kingdom Internal Market (UKIM). The analysis here advances two claims: first, the creation of a statutory internal market represents a strategy to ‘de‐constitutionalise’ the governance of the internal market; and second, as an instrument of ‘economic unionism’, the United Kingdom Internal Market Act is disruptive of, and for, ‘collaborative unionism’ within the political and territorial constitution of the UK.</jats:p>