Theresa May's phone call with Leo Varadkar on Monday was, according to Downing Street, an opportunity to "take stock" of the state of Brexit negotiations.
But it followed reports that Brexit secretary Dominic Raab was demanding that Britain should be able to revoke a backstop within three months of it coming into operation.
Tánaiste Simon Coveney tweeted that a backstop that could be ended unilaterally by Britain was not a backstop at all, a sentiment endorsed by the EU's deputy chief negotiator Sabine Weyand. "Still necessary to repeat this, it seems," she tweeted.
Downing Street has not publicly endorsed Raab’s demand for a unilateral review mechanism for the backstop, and the prime minister’s official spokesman declined to say if Britain was seeking a system of third-party arbitration to determine when the backstop should end.
British negotiators complain that a bilateral mechanism would give the EU a veto on ending the backstop, leaving the UK trapped in a customs union indefinitely.
The European Commission and Ireland both reject the idea of independent arbitration, which the EU says would undermine its autonomy. Ireland has long resisted binding international arbitration of disputes with Britain over Northern Ireland, even writing that exception into the State's acceptance of the statute of the International Court of Justice in 2011.
British and EU negotiators agree on the shape of the backstop, which would take the form of a UK-wide, bare-bones customs union with the EU, accompanied by some customs and regulatory measures specific to Northern Ireland.
Northern Ireland would not be described as part of the EU’s customs territory and the extra customs provisions would be presented as technical measures with no constitutional implications.
Regulatory checks
It remains uncertain, however, if this backstop’s Northern Ireland-specific customs measures will be acceptable to May’s cabinet, to say nothing of the DUP, which is propping up her government.
The bare-bones customs union for Britain would mean that regulatory checks would still be necessary at cross-channel ports like Dover and Calais, but London would not be able to set its own tariffs.
For Conservatives who are both Brexiteers and unionists, it looks like the worst of both worlds, with Britain trapped in a customs union while Northern Ireland is still obliged to follow different rules. The expectation at Westminster now is that the deal cannot be signed off in time for a summit in the middle of this month.
Even if the summit has to wait until the end of the month, however, the deal on offer to Britain will be essentially the same as it is now – and as it was last month when the negotiations were interrupted.