The government is facing another legal challenge over Brexit, this time involving the question of whether it has the right to take the UK out of the European single market.
British Influence, a campaign group, believes it has spotted a loophole that could allow the UK to leave the European Union while remaining a member of the parallel European Economic Area (EEA) organisation – a free trade group that includes all EU countries plus the likes of Norway and Iceland but has fewer political elements.
As a result the campaign group hopes to force the government to go through a separate process to surrender the UK's membership of the EEA, which allows the free trade of goods and services across Europe while also allowing free movement of people.
Effectively, this would increase the possibility of the UK remaining at least partially within the old EU structures, rather than abandoning them completely.
"Why wouldn't you bring this challenge?" British Influence director Jonathan Lis told BuzzFeed News. "The EEA grants us single market access in everything but agriculture and fish. If it can be established that we're members of the EEA in our right then we can't be kicked out."
The UK joined the EEA with the rest of the EU in 1994 at a time when it was never considered that the country would attempt to leave either organisation. However, British Influence hopes to prove that the UK has membership in its own right, rather than simply as a member of the EU market.
While there has been lots of talk of the UK invoking Article 50 to leave the EU, if it was established that Britain had independent membership of the EEA then parliament and the government could potentially have to go through an entirely separate process to declare so-called Article 127 to leave the single market.
Lis said this could strengthen the UK's attempt to strike a post-Brexit trade deal with the EU: "At the moment the EU has all the cards. The first step is establishing if we're in it as part of the EU or in our own right."
The government insists that leaving the EU would automatically result in the end of the UK's membership of the EEA. Remaining in the group could be politically problematic for the government because the UK could then struggle to reduce immigration to its desired level.
There is already another court case – due to be heard by the Supreme Court this month – over whether parliament has to be consulted before prime minister Theresa May can start the process of leaving the EU.
British Influence was founded by a cross-party group of pro-EU politicians in 2012 but Lis said this was not an attempt to subvert the referendum result: "We were pro-Remain, now we're pro-single market. We're not campaigning for a second referendum. We're already in the EEA – why wouldn't we try and stay in it?"
He also said the organisation had the funds for a long legal fight and would theoretically be willing to take the battle all the way to the European courts: "What we're hoping is the government accepts that we could be in the EEA in our own right. If another member of EU decides to challenge this then it would go to the ECJ [European Court of Justice]."