The Northern Ireland Protocol is back in the news this week. The UK government's plan to set aside big parts of it has led to a serious row between the EU and the UK.
British-Irish relations have also been damaged in the fallout. So six years after the UK voted to leave the EU, why has this all not been settled by now?
Here, we answer your questions on the subject.
Remind me, what is the protocol again?
The protocol is part of the Withdrawal Agreement - the international treaty under which the UK left the EU.
It was a compromise to prevent a hard border with checks on goods crossing from Northern Ireland into the Republic of Ireland and the EU’s Single Market.
Under the deal, Northern Ireland left the EU along with the rest of the UK.
But the British government accepted that it would stay aligned with the EU’s Single Market rules for goods.
That allowed the checks to be done at Northern Ireland’s ports instead of along the 300-mile land border.
It has been dubbed 'The Border in the Irish Sea'.
Hasn’t the protocol already been agreed - why is it back in the news?
It’s back in the news because even though the UK government agreed it, it now wants big changes.
Unionists object to the protocol saying it undermines Northern Ireland’s constitutional position in the UK.
They say it has also affected trade because of the complexities for some companies in complying with import rules for goods from Britain.
The UK says it’s also affecting political stability in Northern Ireland, with the row preventing the restoration of power-sharing.
Protocol supporters want it to stay because it gives NI companies unique access to both EU and UK markets - a commercial advantage they want to keep.
They say any issues can be ironed out through meaningful negotiation between the UK and EU.
What is the British government proposing to change?
It is proposing UK legislation that would set aside significant sections of the Northern Ireland Protocol.
It would create green and red lanes for goods coming from Britain. Green lane goods would be destined for sale only in Northern Ireland and would have essentially no checks. Red lane goods would transit Northern Ireland, bound for the Republic or other EU member states.
Paperwork and checks would be needed for these and the data shared with the EU. The problem is essentially one of trust. The EU remains to be convinced that the UK will do what it says it will.
Another big issue is who settles any disputes. The European Court of Justice is where the buck stops for disputes involving European law. The UK wants to change it so that protocol disputes go to independent arbitration – something the EU is unwilling to accept.
In recent days, three of Northern Ireland's main political parties wrote a joint letter to British Prime Minister Boris Johnson rejecting his plan for unilateral legislation on the protocol. It was signed by MLAs from Sinn Féin, Alliance and the SDLP.
How does the protocol affect people on a daily basis?/Will there be some checks along the border?
Most people will tell you it doesn’t actually affect their lives at all. But if you run a business, especially one importing goods from Britain, you may have seen additional cost and complexity.
The DUP says that cost is being passed on to consumers and is increasing prices, but it’s hard to get data that supports that contention. Checks along the border appear very unlikely. There’s no support in any quarter for that.
The British government says most checks can be done "in market", that’s at places like warehouses, well away from the border.
Does it affect the Good Friday Agreement?
That’s a tricky one. The protocol was meant to protect the Good Friday Agreement by ensuring no hardening of the border on the island with facilities for customs and other checks.
The DUP has gone so far as to say that if the protocol problems aren’t resolved it could destroy the 1998 peace agreement.
It points out that not a single unionist MLA supports the protocol in its current form and Northern Ireland doesn’t work unless there’s cross-community consensus on important issues.
The DUP’s opponents say Northern Ireland voted to remain in the EU and the protocol was the answer to a problem not of its making.
The row over the protocol is having a direct effect on the Good Friday Agreement. The DUP is refusing to reinstate power-sharing after the May election until unionism’s protocol concerns are addressed.
Power-sharing at Stormont is one of the three pillars of the Good Friday Agreement, alongside what were meant to be improved cross-border and British/Irish relationships.
Has Britain not broken international law?
Depends on who you listen to. The UK government says it hasn’t, virtually everyone else says it has.
And how exactly does this impact power-sharing in Northern Ireland?
Northern Ireland had an election in May. It should have led to a new power-sharing government. But there’s still no sign of it. The DUP will not re-enter the cabinet - or Executive - until unionist concerns over the protocol are addressed.
Ministers remain in departments, but without an Executive there can be no new government business.
The DUP has also refused to facilitate the election of a speaker for the Northern Ireland Assembly - which must be done under a cross-community voting mechanism. Without a speaker the Assembly is effectively neutered.
How are the EU and Ireland reacting? How are relations?
Terrible. They haven't been as bad for a long time. Minister for Foreign Affairs Simon Coveney said Irish/British relations had reached a new low over the row.
The EU said it has tried to be flexible and offer compromises that the UK has not explored. It's announced that it's restarting a legal action it had paused against the UK and commencing two others citing the UK's failure to build and staff permanent Border Control Posts for checks in Northern Ireland and failing to share appropriate data with it on goods moving from Britain into Northern Ireland. The EU says it remains ready to talk.
What’s this about averting a trade war?
We are some way away from that but it has been talked about. If the worst came to the worst this could lead to a full-scale trade dispute between the UK and the EU.
One option open to the EU would be apply taxes called tariffs on trade with the UK. It would likely retaliate. That’s a trade war.
But there’s no guarantee the UK legislation setting aside the protocol will be passed any time soon. It could take more than a year.
Also, Westminster MPs and members of the House of Lords who oppose the idea of the UK breaking international law - which is what the Withdrawal Agreement is - could water it down significantly.
It will be months before we see how things are really shaping up.
What happens now?
Good question. The UK government is progressing its legislation, and the EU has set out its response.
There is clearly no meeting of minds in the short term.
In the meantime, Northern Ireland is left in political limbo. It looks like there'll be no restoration of power-sharing at Stormont until the protocol legislation is well advanced. Westminster's summer recess is coming up. So don't expect any major movement this side of the autumn.