We are in the market for a “reassurance”.

A clarification, not a renegotiated treaty.

A way of demonstrating that the withdrawal treaty, and specifically its backstop provision, are not a straightjacket that will confine the UK against its will in the EU customs union for ever more.

What then can be done for the UK given the constraints of the treaty? A declaration that the UK can unilaterally repudiate the backstop would undermine the safeguard completely and would be a clear breach of the treaty. Not on.

But a clear explanation of the role and mandate of the little-understood arbitrators, whose binding role is provided for in the treaty to adjudicate a deadlock between the EU and UK over leaving the backstop, is another matter.

EU leaders anxious to help British prime minister Theresa May out of her pickle are keen to offer some comfort. They were not helped, however, by the infelicitous, almost gloating, but erroneous, suggestion by France’s president Emmanuel Macron at the summit two weeks ago that the backstop review mechanism would allow him to hold up the UK’s departure from the backstop unless it did a deal to allow French access to UK fisheries.

The threat was manna to the Brexiteers. Here was the evidence that the UK could be “held hostage” by the EU.

But Macron profoundly misunderstands the treaty backstop review mechanism.

The treaty provides that should one party, either the EU or UK, feel that the time has come to quit the backstop - when another agreement has been reached that does its job of protecting the frictionless border - it can apply to do so to the Joint Committee set up to manage the Northern Ireland protocol implementation.

Should the joint committee, which has equal representation from the UK and the EU, fail to agree, the issue goes to binding independent arbitration.

The treaty makes clear that by law, the arbitrators would only be able to consider two grounds for granting or denying the request - that the parties had genuinely been negotiating an alternative in good faith, and, to quote the British legal opinion, whether the party applying to end the backstop “had acted lawfully in reaching a view about whether the protocol was necessary to achieve its objectives”.

While certainly not a unilateral right to withdraw from the backstop, the provision does ensure that an unreasonable veto by a member state or the EU itself, either in setting the bar too high or prevaricating in talks, would not be able to “trap” the UK in a backstop or customs union. The absence of a fishing agreement would certainly not be grounds acceptable to arbitrators.

A “reassurance” declaration at this week’s summit by the 27 emphasising the role of and independence of arbitrators and of the scope of their mandate in any review of the backstop, could help to clarify the treaty provisions, without changing them, and should be able to answer the “held hostage” fears of at least some of Mrs May’s critics.

The UK and the EU have both made clear repeatedly that they believe that a comprehensive future framework relationship which would do the job of the backstop can be agreed. Eventually. It is necessary now to come up with a means of safeguarding and guaranteeing the frictionless border in the interim. Any “reassurance” declaration from the summit must start and end from that point.