The Brexit backstop has become one of the most contentious elements of negotiations, with no one able to agree on how it’ll work.
In theory, the backstop isn’t a complicated concept but the sensitivities of Northern Ireland, the rest of the UK and the EU muddy the waters.
With little more than 150 days until the March 29 Brexit deadline, it’s crunch time now – whether the government is ready or not.
And it all seems to hinge on the backstop.
What is the Brexit backstop in simple terms?
The backstop is a sort of last resort, safety net or insurance policy.
The backstop is meant to ensure no matter what happens with the rest of the negotiations, there won’t be a hard border between Northern Ireland and the Republic.
So, even if the rest of the UK leaves the EU with no trade or security arrangements, there won’t suddenly be border checks and restrictions on the island of Ireland.
At present, goods and services are traded between the two jurisdictions with few restrictions.
As the UK and Ireland are currently part of the EU single market and customs union, products do not need to be inspected for customs and standards, but after Brexit, all that could change.
Both the EU and UK have said they don’t want a hard border and want the backstop safety net in case all other negotiations fall apart.
But the problem is that even the backup negotiation is proving impossible to reach – so far, all that has been agreed is a need for a backstop.
And the EU won’t agree to a transitional period for Brexit implementation and substantive trade talks until the backstop is in place.
Both sides agree the backstop will need to achieve the following: maintaining cross-border cooperation, supporting the all-island economy and protecting the Good Friday peace agreement.
But beyond that, both sides are at an “impasse,” as Theresa May called it.
What does the EU want?
The EU has proposed a backstop that would mean Northern Ireland staying in the EU customs union.
Chief negotiator Michel Barnier has continually said this backstop can only apply to Northern Ireland, not the rest of the UK.
But the UK is radically opposed to this plan.
The reason is that, if the EU gets its way, there will essentially be a customs and regulatory border down the middle of the Irish Sea, cutting off the rest of the UK.
Any separate status for Northern Ireland from the rest of the UK is seen as potentially damaging to the union as a whole.
Theresa May has sworn this is something she will never agree to.
And leaving the customs union and single market are also the UK’s red lines in negotiations, so they won’t agree to allow the whole UK to stay in.
So what does the UK propose?
Theresa May has suggested a backstop that would see the whole UK remaining aligned with the EU customs union – but only for a limited time after 2020 (she has avoided specifying how long she thinks this would be) while an alternative solution is negotiated.
But the EU firmly refuse to allow this time-limited option, as they argue the guarantees the backstop offers will be needed for as long as an alternative solution is not found.
However, Mr Barnier did not entirely rule out some sort of long-term customs relationship with the UK.
But Mrs May is not only facing pushback from the EU.
Conservative MPs have been angered by the suggestion that the UK could be tied to EU rules for the long term.
And the DUP, who Mrs May is dependant on to pass her final Brexit bill in parliament, have repeatedly said they would not accept any additional Northern Ireland-only checks no matter where or how they take place.