Yet quietly, officials were congratulating themselves on Thursday about making incremental progress on a closely interlinked issue the Irish border.
After media reports overnight, Theresa May issued a carefully worded statement as she arrived in Sofia, Bulgaria, on Friday, repeating the familiar statement that Britain will be leaving the customs union.
But Whitehall sources confirmed that away from the deadlocked Brexit war cabinet her strategy and negotiations subcommittee a fresh proposal has been agreed that Britain hopes would avoid a hard border in Northern Ireland, if all else fails.
This backstop was written into the December agreement between London and Brussels, at the request of Ireland. It commits Britain to maintain full alignment with those rules of the internal market and the customs union which, now or in the future, support North-South cooperation, the all-island economy and the protection of the 1998 Agreement.
What that will mean in practice needs to be spelled out in detail. The EU has published its own definition, which would involve Britain remaining in the single market and customs union but May told parliament no prime minister could ever agree to that.
If the backstop had to be enacted, Britain would agree to maintain the common external tariff the import tax levied on goods coming into the EU, which is hated by the Brexiters and align its regulations with Europe’s.
But Britain would seek to opt out of the common commercial policy, which prevents member countries from negotiating independent trade deals.
The trade minister, Liam Fox, has been touring the world to play up the benefits of global Britain though presumably these agreements would only kick in once Britain has stopped applying the external tariff, as Fox will have little to offer before then.
The government hopes this approach will meet the definition of the backstop set out in the December agreement – and that it could help win over Dublin, which would put pressure on Brussels to accept it.
Of course, none of this changes the fact that there are two conflicting visions of Britain’s post-Brexit customs arrangements within May’s inner cabinet.
HMRC officials have warned that even once a decision is made, neither of these options will be ready for the end of the transition in December 2020.
It is unclear whether Brussels will be prepared to accept this half-in, half-out approach to the customs union – but it at least helps Downing Street to rebut claims that the government is paralysed in the face of Brexit.
To that end, David Davis’s DexEU has also announced that will publish a 100-page white paper in in coming weeks, setting out what the government hopes to get out of the negotiations.
If May really wants to get on the front foot before parliament breaks up for the Whitsun recess, there is one more gamble she could take.
On Thursday, while announcing the Commons business for the week ahead , the leader of the Commons, Andrea Leadsom, set aside time for considering Lords amendments on Tuesday and Wednesday, if necessary.
That just about leaves open the idea that she could bring the EU withdrawal bill, which has been peppered with amendments by rebellious peers, back to the Commons next week.
It would be highly risky, which is not May’s usual style – but if, as backbench Brexiters insist, she could win the contentious votes, she could leave for her break on the front foot over Brexit for the first time in months.