The Court also agreed to the applications by the Welsh and Scottish Governments to intervene. An intervention in an ongoing legal case can be applied for by anyone who has some right or interest in it and will not unduly prejudice the original parties in the case.

The IWGB is an independent registered trade union founded in 2012 whose members are predominantly low paid British and migrant workers, many of them citizens of other European Union (EU) Member States.

The IWGB will provide a written submission up to a maximum of 20 pages, and will seek the opportunity to present brief oral submissions of no more than 45 minutes, on issues surrounding the UK’s decision to leave the EU, which it believes directly affects its members and which necessitate an Act of Parliament before the UK leaves the EU.

These include the 3.3 million citizens of other EU Member States who, in reliance upon their EU free movement and citizenship rights, have moved to the United Kingdom (UK) to live and work.

They will ask the Court to rule that the Government debate the rights that its EU migrant worker members will inevitably lose following the triggering of Article 50 of the Treaty on European Union (TEU).

The IWGB also has, and is currently actively recruiting more members resident in Scotland who were entitled to vote in elections to the Scottish Parliament. EU migrant workers of voting age who are resident in Scotland also form part of the electorate to the Scottish Parliament.

The IWGB seeks to ask the Court on the operation of the devolutionary settlement in Scotland and how the Article 50 TEU notification would impact on the Scottish constitution.

It also seeks the Court to consider how Article 50 TEU will affect the rights of the union and its members in the field of labour relations and collective bargaining, currently protected in the UK both as a matter of Convention law and as a matter of EU law.

Dr Jason Moyer-Lee, the General Secretary of the IWGB said:

“Brexit represents possibly the biggest assault on workers' rights and migrants' rights in this country for a generation. And the idea that this Government wants to launch this assault without even an act of Parliament, despite all the Brexiters' rhetoric about parliamentary sovereignty, is hypocritical and shameful.

“The IWGB is not prepared to remain quiet while our members' rights are stripped away unlawfully, and as such we will be intervening in the Supreme Court."

Richard Stein from the public law team at Leigh Day who is representing the IWGB in their intervention said:

“The issues raised on behalf of the IWGB raise additional matters which will assist in deciding the outcome of this hugely important constitutional case.”