The last stumbling block in the Brexit negotiation

Irish police officers patrol the border between Ireland and Northern Ireland in the town of Bridgeend in April 2019.CLODAGH KILCOYNE / Reuters

The latest Brexit hieroglyph is made up of two bona fide assumptions and a legal decision with a suspicious scent of political maneuvering.

First assumption: once outside the EU internal market, the UK must order its own internal market.

The autonomous governments of Scotland, Wales, or Northern Ireland are going to regain their own competences - fishing, agriculture, trade, etc - that until now Brussels regulated.

London aspires to develop a single market law that establishes common rules and prevents unfair competition and potential distortions.

Second assumption: international treaties have the force of law and must be respected.

The Withdrawal Agreement signed between the United Kingdom and the EU in January this year established that Northern Ireland would remain - until a definitive solution is found - within the internal community market, subject to its rules.

It was the way to prevent the reestablishment of a new border between the two Ireland (it should always be remembered that the Republic of Ireland is the western border between the EU and the United Kingdom) that would resurrect the threat of violence.

The maneuver that has jeopardized a future trade agreement between London and Brussels is, according to the Boris Johnson government, a mere technicality to connect the dots and avoid legal loopholes;

and according to its critics, a trap to blatantly skip the obligations under the Withdrawal Agreement.

It affects two very specific issues: customs declarations and state subsidies to industry.

In theory, any good whose origin is Northern Ireland and its destination is elsewhere in the United Kingdom, must have the corresponding export form, and vice versa.

And in theory too, any public aid to a Northern Irish company must be notified to Brussels to gauge whether it is an unfair competitive advantage.

In the text of the new UK Internal Market Act, the Johnson Government has introduced two clauses that alter both assumptions.

It will be the exclusive responsibility of the Minister of Commerce to decide what should be considered state aid and what not when notifying Brussels.

And it excludes Northern Irish companies from filling in any customs forms when they export goods to the rest of the UK.

It is Johnson's way of saving face and keeping his promise that Northern Ireland would not be treated differently from the rest of the country, as Eurosceptic conservatives and Northern Irish unionists continue to claim.

Downing Street assures that the accusation of having breached the legal validity of the Withdrawal Agreement is false, that the United Kingdom fulfills its commitments and acts "in good faith", and that, in the words of the Minister of the Environment, George Eustice, this same Monday, "the same treaty recognized in its text that certain matters should be specified and outlined in the future."

The consequences of the move, however, can be catastrophic.

In the short term, because they can derail current negotiations already very stranded.

In the long term, because it will be difficult to erase that future stain on the UK's reputation as a trusted international player.