As Sir Stephen Laws QC, Richard Ekins and I explained in a paper published by Policy Exchange this Friday, the good faith and best endeavours obligations in the Withdrawal Agreement and Northern Ireland Protocol (the backstop), in addition to the Joint Instrument agreed at Strasbourg, offer the UK far greater legal comfort than seems to be appreciated. This is not enough for some sceptics in the ERG who want to be reassured that, if the worst came to worst, the UK could leave the backstop unilaterally.
There has been much discussion about Article 62 the Vienna Convention on the Law of Treaties (VCLT), which deals with the right of states to terminate treaties when there is a fundamental change of circumstances. Some commentators, including the so-called 'Star Chamber' of MPs and Martin Howe QC, dismiss the possibility of the UK ever being able to exit the backstop by relying on this route. Others, most notably Lord Pannick QC, have taken a different view.
For a case under Article 62 to succeed, a number of conditions must be satisfied. In particular, a change of circumstances must be fundamental and not foreseen by the parties, and the effect of the change must be to radically transform the obligations of one of the parties.
To illustrate how impossibly high the VCLT bar is, sceptics have pointed to the 1997 judgment of the International Court of Justice in the Gabčíkovo-Nagymaros dispute between Hungary and Slovakia. The 'Star Chamber' has noted, for example, that in this case not even 'the fall of the Soviet Union, disappearance of the Warsaw Pact, and dissolution of Czechoslovakia' were enough to justify Hungary’s attempt to terminate the treaty. This precedent also prompted Professor Philippe Sands QC, who was counsel for Hungary, to conclude that a UK attempt to leave the backstop based on fundamental change of circumstances would be 'utterly hopeless'.
However, Hungary’s argument, while unsuccessful in the end, was not 'hopeless' (otherwise their lawyers would have not argued for it), and there is a good reason why it failed. The Gabčíkovo-Nagymaros dispute arose from a treaty concerning a dam project for controlling floods and improving navigation on the river Danube. As the Court explained, those otherwise very significant social and political changes 'were not so closely linked to the object and purpose of the Treaty that they constituted an essential basis of the consent of the parties'. This is hardly surprising. It is difficult to see why the advancement of Marxism-Leninism or the defence of the Warsaw Pact should have changed the countries' reasons for signing up to the treaty.
The position would be evidently different – and quite possibly stronger for the UK – if, contrary to the UK’s and EU’s stated expectations and intentions, the backstop became permanent, and even ended up undermining the very reason it was conceived (i.e. protecting the Good Friday Agreement).
It has also been argued that the UK could never succeed in demonstrating that the change was 'unforeseen' given fears about the permanent duration of the backstop are being publicly discussed now. But the point is that the express, and emphatic, intention and expectation of the parties is that the backstop, if it ends up being needed, would have to be temporary. This intention is spelled out in the text of the Withdrawal Agreement, and developed and detailed in the Joint Instrument. An event that is imagined or feared is not necessarily one that is foreseen in the scheme of a treaty. Moreover, the EU could not credibly contend that it predicted the backstop to last forever, as this would call into question its good faith obligations.
Some seem to be concerned about the fact that the EU is not a party to the Vienna Convention. But this concern is a non-starter. The 'Star Chamber' correctly observes on this point that 'the VCLT is generally regarded as codifying pre-existing customary international law and hence the same result is likely whether or not the VCLT as such applies.'
Another argument is that the UK would never be able to satisfy the requirement that the effect of the change would radically transform the UK’s obligations. The obligations under the backstop are designed, intended and expected to be temporary; in the Joint Instrument, the UK and EU even say that they do not wish them ever to be used. A delay resulting effectively in 'permanence' would constitute a radical transformation of these obligations. If I agree to let someone use my house for a temporary but unspecified period, it cannot be seriously suggested that it makes no difference whether that person stays for a month or five years.
Critics of the deal should look again at the position of the backstop, which has improved since Theresa May won assurances at Strasbourg. What is not available is a simple unilateral exit mechanism from the backstop, which some were hoping for. The current package – comprising the Withdrawal Agreement, the Protocol, the Joint Instrument and the applicable principles in the VCLT – may be described as providing 'sub-optimal mutual legal reassurance'. Each side can be confident that it would have strong arguments to defend its interests in its 'worst case scenario' – for the EU and the Irish, if the UK arbitrarily attempted to leave the backstop at a time of its choosing; and, for the UK, if the EU attempted to trap the UK into a de facto permanent backstop.