Boris Johnson is facing a major Brexit test with the future of Eurotunnel operations at stake, it has emerged. The EU wants the UK to drop its opposition to a role for the European court of justice in British affairs to ensure trains keep running between France and the UK after Brexit is implemented on 1 January. The European commission has this week asked the European parliament and the European council to officially mandate France to urgently negotiate a new bilateral deal with the UK giving the ECJ the powers to resolve future disputes between the two countries as “union law would not longer be applicable to the part of the channel fixed link under the jurisdiction of the United Kingdom” after Brexit. Unless there is an overarching deal with one body responsible for legal disputes regarding the entire 30-mile (50km) tunnel there will be chaos, insiders say. “It would mean train drivers would have to have two sets of qualifications to drive on the British and French side of the tunnel. It would affect how you operate the tunnel with potential for divergence in the future on everything from signalling, voltage, the radio systems, the signalling system, ventilation, hydraulics. It would be like driving on the left- and right-hand side of the road at the same time,” said a source. The EU’s plan to keep the ECJ as an arbiter in disputes will be anathema to Downing Street. A senior official involved in the Brexit negotiations says there can be “no halfway house” on the ECJ and that Michel Barnier’s team have recently accepted it is a “non-starter”. The commission’s move follows a request on 16 July by France informing it that “it would like to negotiate an agreement supplementing the Treaty of Canterbury” signed by Margaret Thatcher and François Mitterrand in 1986 to facilitate the undersea tunnel. One option is to make the international court of arbitration in The Hague the apparatus for dispute resolution. It was used in 2007 when the then Channel Tunnel Group won its £35m compensation claim against the two governments over losses suffered because of damage and security expenses arising from “multiple incursions” of migrants who were living in the Sangatte refugee camp near Calais. Experts say that finding a way of adjudicating over future disputes between the bloc and the UK without some role for the ECJ is almost impossible and point out that it will be involved in disputes over the Northern Ireland protocol and citizens’ rights. “From the EU’s point of view it would be very odd to have a railway in its territory that was not governed by EU law, from the UK’s point of view it would also be odd to have a railway in its territory not governed by UK courts but the Treaty of Canterbury provides for one legal regime,” said Steve Peers, law professor at the University of Essex. On the wider issue of the ECJ, Catherine Barnard, professor of EU law at Cambridge, thinks “it is going to be very difficult to exclude the ECJ unless we have such a thin trade deal that it’s not worth the paper it’s written on with no principles of EU law engaged at all”. It is understood that one option discussed at the negotiating table is a political mechanism for dispute resolution, say insiders. But this comes with huge and expensive risks of “whack-a-mole” trade wars. If it was up to governments to settle disputes, the UK could decide to impose tariffs on German cars, for example and the EU could retaliate by slapping tariffs on Scottish whisky, just as Donald Trump threatened earlier this year. “If you have a problem in one area you shouldn’t be able to retaliate in another completely unrelated area,” said a senior UK official involved in the talks who hinted at an overarching agreement but with specificity on “which bits of the treaty can be suspended in response to the difficulties”. “This could be an area for wriggle-room. It means we could say to the EU we will keep the EU happy by having one big treaty but then say the dispute resolution mechanism only applies to areas 1, 2 and 3 to stop the retaliation [or prospect of trade wars],” says Barnard. A department for transport spokesperson said it supported measures to secure the continuation of critical services through the Channel Tunnel regardless of the outcome of Brexit talks adding: “We are absolutely clear that we will protect our national interests in any bilateral arrangements and they will fully respect the UK’s status as an independent, sovereign nation.”