Following a vote by the House of Commons in favour of a motion finding ministers in contempt for their failure to publish the full legal advice on the withdrawal agreement, the Attorney General made available to Parliament on 5 December 2018 the legal advice provided to the Cabinet on 14 November 2018 on the legal effect of the withdrawal agreement.The government has also published the legal advice.
One of the issues that the legal advice addresses is the legal effect of the Protocol on Ireland/Northern Ireland. Most of the Protocol will only apply from the end of the transition period (or any extension of it), and then only to the extent that the Protocol provisions are not superseded by agreements on the future UK-EU relationship
The legal advice also includes the following points:
The Protocol does not provide for a mechanism that is likely to enable the UK lawfully to exit the UK-wide customs union without a subsequent agreement. The Article 19 review mechanism, which allows termination by mutual consent, adds little (other than procedurally) to the international law position, under which the parties could always terminate or amend the agreement by consent.
In international law, the Protocol would endure indefinitely until a superseding agreement replaced it, in whole or in part, despite statements in the Protocol that it is not intended to be permanent, and the intention of the parties that alternative, permanent arrangements should replace it. The withdrawal agreement cannot provide a legal way of compelling the EU to conclude a superseding agreement.
It is unclear whether Article 50 provides an adequate legal basis in EU law for the Protocol. This uncertainty will increase the longer the Protocol lasts. The EU had previously argued that Article 50 could not provide the legal basis for a UK-wide customs union, or at least not once it becomes clear that it is not just a temporary bridge to a more permanent future arrangement.