What role does the European Court of Justice play in the disagreement over the NI Protocol?

If talks between the UK and EU over the Northern Ireland Protocol are to be successful, they clearly need to take us to a position that gives power-sharing the best chance of resuming in Stormont.

So, as negotiations intensify, what will it take to bring the Democrat Unionist Party (DUP) back to the table?

NI's second largest party, which has refused to serve under a Sinn Fein first minister ever since the nationalists won last May's elections, have made quite clear what they want by setting out seven tests.

The overriding sense that unionists feel since the protocol was agreed is clearly one of loss and identity, and their sense of an equal place within the UK.

The tests they've laid out to deal with that overwhelmingly focus on is the question of trade and what the protocol has meant for trade in NI. 

In fact, the second (avoiding diversion of trade), the third (not having a border in the Irish sea), the fifth (scrapping any new checks of goods going from GB to NI or back again), and the sixth (having no new regulatory borders) are all along those lines. 

Meanwhile, the first test (ensuring that everyone in the UK is entitled to the same privileges) and the seventh (providing consent to people in Northern Ireland if there is any diminution of NI's status in the UK), are closely linked to them - by underlining the sense of loss that unionists feel because of the practical implications of the protocol. 

All of which explains why I'm hearing that the heavy focus of this attempt to turbo-boost negotiations is on solving those specific problems.

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The thing I've heard much less about is a focus on appeasing anger around arbitration and the role of the European Court of Justice (ECJ). 

And that means that - while there are unquestionably still outstanding issues - suggestions of the EU signing up to the UK's proposal of a red and green lane model to prevent checks on goods headed from GB to NI, is likely to be seen as important progress in Whitehall. 

A solution in that area would certainly appease some of the torment I saw in a recent visit to Belfast over the protocol.

At one business - a chain of nurseries - the owner who was a unionist described being unable to import flowers from GB to NI anymore and instead having to turn his trade 90 degrees to buy produce from the Republic of Ireland instead.

Although he could ultimately make it work economically, just about, he felt as if the shift had torn away some of his identity.

Now, that is not to say that the DUP do not care about the ECJ. DUP leader Jeffrey Donaldson has spoken about the role of the European court when asked about the one test I missed out: "Fourthly new arrangements must give the people of Northern Ireland a say in the making of the laws which govern them."

Asked about it - he said it wasn't acceptable for NI to fall under the jurisdiction of a court over which it has no control. 

But it is certainly striking that his seven tests make no explicit mention of the ECJ. 

Should the government bring back a deal that solves many of the problems on trade and so addresses well six of the seven tests - but falls short on the ECJ - what would that mean politically? Could the DUP stomach that? Some say perhaps. 

Although, there is another group who are very explicit about the ECJ - and know how to cause Conservative prime ministers a headache. And they are Tory backbenchers in the European Research Group.