The report, The invoking of Article 50, states that the government should not trigger Article 50 without consulting parliament. The Committee says it would be 'constitutionally inappropriate' and would set 'a disturbing precedent' for the government to act on the referendum without explicit parliamentary approval.

The referendum result was ‘clear’ with 51.9% of voters in favour of leaving the EU on 23 June, the Commission states, adding that parliament is responsible for ensuring the government implements that result and takes forward Brexit negotiations in a way that achieves the best possible outcome for the UK as a whole.

Parliament and the government will need to work together with a mutual respect for each party's constitutional role—and that starts with the Parliamentary involvement and assent for the invoking of Article 50, stresses the committee report.

The report points out that although the EU referendum was, in legal terms, advisory, it was accompanied by a clear undertaking by the government, based on a manifesto commitment, to implement the decision reached in the referendum.

Following heated debate about whether MPs should be allowed to vote on the triggering of Article 50, the Committee states that parliament should:

1. play a central role in the decision to trigger Article 50; and
2. have a key role scrutinising both the Brexit negotiations and in approving the final deal between the UK and EU.

Article 50 of the Treaty on European Union sets out how member states may withdraw from the European Union. It states that ‘any member state may decide to withdraw from the Union in accordance with its own constitutional requirements’.

Before the referendum, a paper published by the government reviewed the suggestion that the UK could leave the EU by simply repealing the European Communities Act 1972, but this was rejected as a ‘breach of international and EU law to withdraw unilaterally from the EU (for example, by simply repealing the domestic legislation that gives the EU law effect in the UK). Such a breach would create a hostile environment in which to negotiate either a new relationship with the  remaining  EU  member  states,  or  new  trade  agreements  with  non-EU countries’.

Judicial review

There is also a judicial review into the case for requiring MPs to approve Article 50 through an Act of parliament. The case is being brought by law firm, Mishcon de Reya, on behalf of a group of clients. Following publication of articles on the subject this week Mishcon de Reya has retained Baron David Pannick QC and Tom Hickman to act as counsel in this action, along with Rhodri Thompson QC and Anneli Howard.

Kasra Nouroozi, partner, Mishcon de Reya said: ‘We must ensure that the government follows the correct process to have legal certainty and protect the UK constitution and the sovereignty of parliament in these unprecedented circumstances.

‘The result of the Referendum is not in doubt, but we need a process that follows UK law to enact it. The outcome of the Referendum itself is not legally binding and for the current or future Prime Minister to invoke Article 50 without the approval of parliament is unlawful.’

An administrative hearing was held on 19 July which laid out a timetable for the claims, with a hearing date likely to be set for mid or late October. Any interested parties or interveners have until 21 September to file their skeleton arguments with the defence's case due to be submitted by 30 September.

Reversal

In considering Article 50, the Committee concluded that it is unclear whether Article 50, once triggered, could be unilaterally reversed by the UK.

The report states that parliament should act on the assumption that triggering Article 50 would be irreversible, and that Article 50 should be triggered ‘only when it is in the UK's best interests to begin the formal two-year negotiation process’.

Lord Lang of Monkton, chairman of the Committee, said: ‘The referendum result was clear and it is right that the government are preparing to take Britain out of the EU. However, our constitution is built on the principle of parliamentary sovereignty and the decision to act following the referendum should be taken by parliament.

‘Parliament should be asked to approve the decision to trigger Article 50—a decision which will start the formal process of the UK leaving the EU and set a deadline for the UK's exit.

‘Parliament's assent could be sought by means of legislation or through resolutions tabled in both Houses of Parliament. An Act of Parliament would give greater legal certainty and could be used to enshrine the "constitutional requirements" required by Article 50, allowing for the setting of advantageous pre-conditions regarding the exit negotiations to be met before Article 50 could be triggered. A resolution could be simpler and quicker to secure but might not provide the same watertight legal authority. We consider that either would be a constitutionally acceptable means of securing parliamentary approval for the triggering of Article 50.’

He added: ‘We all want the negotiations to produce a deal that works for both the UK and the EU, and Parliament must be involved in holding the government to account in delivering that.’

The 20-page House of Lords Select Committee on the Constitution report, The invoking of Article 50, is available here.