Campaigners will be kicking off the legal process today to bring a High Court case on whether the UK's departure from the EU also spells its departure from the Single Market.
While government argues the UK will automatically leave the Single Market once the Brexit process is complete, the new case's claimants contend government will not only need to trigger Article 127 of the European Economic Area (EEA) agreement to do this but will also need to seek approval from MPs to do so.
"For the City, staying in the Single Market, even as a transition period, is vital," Peter Wilding, chair of pressure group British Influence who is bringing the case along with lobbyist and Leave voter Adrian Yalland, told City A.M.
There has been some concern from City surrounding whether passporting rights for access to the EU markets will be secured and whether a transition period, which could extend rights for enough time for firms to put alternative arrangements in place, will be set up.
Late last week, the Financial Times published a leaked memo from David Davis, where the Brexit secretary revealed he was not interested in securing a transition period as part of the exit deal, but could be convinced to put one in place if it were to come at the request of the EU.
Meanwhile, writing in today's City A.M., Dr Savvas P Savouri, chief economist at Toscafund Asset Management, argues the other EU member states should be willing to offer a soft Brexit option because of the extensive financial benefit the UK as a trade partner brings to their nations.
However, Shanker Singham, chairman of the Legatum Institute's special trade commission, told City A.M. the idea the UK had to be an EEA member to keep Single Market access "is not correct", while ditching EEA membership would allow the UK to negotiate bespoke trade deals.
"What people need to be talking about is access to the Single Market, which is different to membership," Singham said.
In addition to the new case headed to England's High Court, a crowdfunding campaign launched by lawyer Jo Maugham to bring a case in the courts in Ireland reached its £70,001 stretch target yesterday.
Maugham's case will seek clarity on whether Article 50 can be revoked once notice is given as well as whether leaving the EU also means the UK will have to leave the EEA.
A government spokesperson said: "The UK is party to the EEA agreement only in its capacity as an EU member state. Once the UK leaves the EU, the EEA agreement will automatically cease to apply to the UK."
The new legal action has been revealed as government winds down from its four-day appeal of the Article 50 decision to the Supreme Court. In November, a trio of judges in the High Court ruled government could not start the withdrawal process from the EU without an Act of Parliament being put in place first.