Lord Lilley is a former Secretary of State for Trade & Industy and for Social Security.

First and most fundamental: the Protocol is intrinsically temporary.

The EU and its apologists argue: “You negotiated the Protocol, it’s permanent, you’re stuck with it. You cannot expect the EU to renegotiate it.”

But this ignores the fact that legally the Protocol is not a permanent arrangement. It must eventually be replaced or lapse. The EU itself said that Article 50 did not provide a legal base for it to enter into a permanent relationship on trade and co-operation. It only allows for the divorce terms and temporary or transitional arrangements to smooth departure.

The Protocol could be agreed under Article 50 only because it was temporary – needed not least because there was no certainty that a permanent trade and cooperation agreement between the UK and EU would be in place by the time we left the EU.

The EU refused Theresa May’s request to negotiate our future trading relationship in parallel with our withdrawal on the grounds that the EU could not legally agree a permanent trading and cooperation agreements under Article 50. Such agreements could only be done (under Article 218) with non-member states.

The UK had therefore to complete its Withdrawal Agreement under Article 50 before it could become a non-member state and even start negotiating a permanent agreement covering trade and cooperation.

So, either the Protocol is temporary or the sequencing of negotiations on which the EU insisted was based on a falsehood and bad faith.

The then Attorney General explained that: “Article 50 of the Treaty on European Union does not provide a legal basis in Union law for permanent future arrangements with non-member states.”

The original Protocol itself spelt out that “the Withdrawal Agreement, which is based on Article 50 TEU, does not aim at establishing a permanent future relationship between the Union and the United Kingdom”.

This is equally true of the Protocol in the final Withdrawal Agreement since it, too, is “based on Article 50 TEU”. Article 13.8 of the final Protocol specifically envisages the replacement of the Protocol by a subsequent agreement.

Nor does the provision in the final Protocol for approval or rejection by the Northern Ireland Assembly alter the issue. Even if the Assembly endorses the arrangements set up under the Protocol (which was an agreement between the EU and the whole UK, not just Northern Ireland) that would not itself change its transitional nature.

The temporary nature of the Protocol is a matter of EU law. The then Attorney General told Parliament that were the Protocol was not replaced it would be vulnerable to challenge in the EU’s own Court. If, as the EU claimed, the Protocol gave unique advantages to Northern Irish firms, other EU Traders who felt disadvantaged by the Protocol “are likely to beat a path to the door of the Commission and the Court, and there to say, ‘Didn’t you say that article 50 is not a sound legal foundation for this arrangement?’ And I tell you frankly, Mr Speaker, they are likely to win.”

The UK, as a non-member state, could not initiate such legal action. But there is no need to seek a judicial ruling since the EU itself has always recognised that Article 50 means it can only be temporary. If the EU now say: “we may have said it was temporary then but there is nothing you can do about it now”, they will demonstrate that the Protocol was negotiated in bad faith and justify the UK in taking unilateral action to replace it.

More positively, we should remind the EU of their position that the Protocol is transitional and therefore seek under Article 13.8 of the Protocol to replace it by an agreed permanent arrangement.