I’ve been having a look at some different types of treaty termination clauses today, to try to get a sense of how you might draft a treaty providing for a “temporary” customs union that has no end date in it.
(thread, probably longish)
(thread, probably longish)
I suspect there will be two elements. First, a “termination clause” in the backstop, providing for the process by which it could cease to have effect. Second, a obligation in the withdrawal agreement to negotiate a future relationship that would obviate the need for the backstop.
What flavours of fudge are available for the termination clause? The late foreign office legal adviser Anthony Aust wrote this very helpful taxonomy. opil.ouplaw.com/view/10.1093/l…
Aust gives us four types. First, “indefinite duration with right to terminate”. This is, I think, much like Article 50: any state may withdraw/terminate by written notice of X period.
Second, the more restrictive “indefinite duration with *conditional* right to withdraw”. E.g. the Chemical Weapons Convention 1993 below – condition highlighted. This could help but kind of hard to imagine what the condition justifying unilateral withdrawal would be. 
Third, “duration until a specific event”. If the “specific event” is the conclusion of a later, superseding treaty, then this could obvs help. E.g., here’s a bit of the Single Convention on Narcotic Drugs 1961.
Also note that A59 of the Vienna Convention on the Law of Treaties specifically provides for “termination by conclusion of a later treaty”.
Fourth, “comprehensive clauses”. These say: it will be in force for a minimum initial term of X years, and thereafter shall remain in force *until* either party gives Y months’ notice of termination. These aren’t much help, I don’t think.
Obviously you could bolt some of these on top of each other in language that doesn’t sound like it anticipates the backstop coming into force. So, something like:
Then, question would be, do you include a unilateral withdrawal clause buttressed by some vague condition, like "(3) Any contracting party may withdraw by serving notice of X months , if it considers that extraordinary events have… rendered the backstop… unsustainable?" Idk.
Then, I think you buttress that with an obligation in the withdrawal agreement to negotiate a super-duper future relationship in good faith.
These are common enough. Eg the GATT, a bit of WTO law, says that “Members shall enter into successive rounds of negotiation ... with a view to achieving a progressively higher level of liberalization.”
There are some interesting examples of such obligations being litigated. E.g., Greece argued that under Article 19 of the Agreement on German External Debts of 1953," Germany was obliged negotiate to settle outstanding claims. Germany disagreed and it went to arbitration.
The tribunal said the below things, incl “an agreement to negotiate implies much more than mere willingness to accept the other side’s capitulation”.
(source: repository.law.umich.edu/cgi/viewconten…)
(source: repository.law.umich.edu/cgi/viewconten…)
But ultimately, an obligation to negotiate still cannot be an obligation to conclude an agreement and, in any case, hard to see the either side taking the other to court over a failure to comply with a duty to negotiate a trade deal. This obligation would be a signalling thing.
You'd probably also stick something non-binding in the political declaration about how no one wants the backstop to come into force etc etc. And there are probably other clever fudges I haven’t spotted or come across. /ends
