It cannot be over emphasised just how extraordinary the demands for a continued role for the ECJ in post-Brexit Britain actually are. As from 20 March 2019 or, at the very latest, from the end of the transition period, the ECJ will convert from being a joint court in which the UK (and a British judge and Advocate-General nominated by the UK) play an equal part, into being a wholly foreign court established under the EU Treaties over which the UK will no longer have any degree of control. Nor will the UK have any say in the appointment of the judges of the court. It is extremely rare for any sovereign state to submit in an international treaty to adjudication of disputes by the courts of the other party to the treaty. The reasons are obvious. Such acceptance of a party to a treaty of the jurisdiction of the domestic court of the other treaty party is i. demeaning and degrading to its status as a sovereign state, and ii. carries with it the practical and very real risk that such a court will be biased and partial in its rulings.
The resolution of disputes by binding international adjudication is of course both a common and often necessary feature of bilateral and multilateral treaties. Adjudication can be by bilateral tribunals or arbitral bodies set up under a specific treaty, or sometimes by permanent international courts or bodies, such as the International Court of Justice (ICJ) at The Hague, or the WTO Disputes Panels and Appellate Body. In all such cases, great care is taken to ensure that the body is balanced between the parties.
International adjudication by an impartial and balanced tribunal is the general and near universal international practice. It is also the general practice of the European Union in its treaties with non-Member states (so-called “third countries” one of which will be the UK from 20 March 2019). The EU has upwards of 50 trade or association agreements with third countries. Of these there are only two which come close to imposing ECJ jurisdiction on non-Member states, and only one creates direct ECJ jurisdiction over another country. The EU-Turkey customs union agreement requires Turkey to follow the case law of the ECJ in applying the common rules of the customs union. This requirement arises from the special nature of a customs union, which of necessity requires all customs authorities at its external borders to enforce and interpret the common rules in a rigidly uniform way.
The second EU external agreement which effectively imposes ECJ decisions on non-Member states is the EEA Agreement. This is done in order to ensure that the common rules of the EU internal market are interpreted consistently across the EU and across the EEA States. But even in this case, there is no direct jurisdiction of the ECJ over the non-Member states which belong to the EEA: instead, a special EFTA Court has been established consisting of judges from Norway, Iceland and Liechtenstein which interprets the rules of the internal market in their application to those countries.
The UK Government has made clear that the UK will leave both the EU single market and the customs union. Neither the EU-Turkey customs union agreement nor the EEA Agreement can in consequence serve as a model for the future EU-UK trade relationship.
The UK Government should therefore unequivocally reject any suggestion for continued ECJ jurisdiction further and beyond the accord reached in the phase I negotiations. Not even tiny Andorra or San Marino accept the jurisdiction of the ECJ and instead follow a normal international dispute settlement procedure in their trade relations with the EU, under which disputes are decided by a panel of three arbitrators, one appointed by each side and the chairman being jointly appointed.
Not only is it largely unprecedented for a sovereign State to accept the jurisdiction of the domestic court of another state or international organisation of which it is not a member. There is also a very real prospect that the ECJ would not discharge that function impartially.