Theresa May’s quest for a “Canada plus” deal in Brexit talks has run into serious legal obstacles and may ultimately prove impossible, risking bitter disappointment and a political crisis next year as reality hits home.

Trade lawyers and European officials warn that even if the EU wants to grant the UK a bespoke deal that preserves unfettered access for goods and services, it cannot do so without granting parallel concessions to Canada, South Korea, and other countries that have free trade agreements. This would open up a Pandora’s Box.

“It is a minefield. Financial institutions are fully of aware of the problem but we have not yet heard anything from the Government,” Chris Bryant, an EU expert at lawyers Berwin Leighton Paisner.

Theresa May stated in Florence last month that a deal based on the Canadian CETA arrangement would not be acceptable for Britain since it would restrict trade and amount to a step backwards. “We can do so much better than this,” she said.

Downing Street is pursuing a “Canada plus, plus, plus” model that goes much further and aims at replicating the EU Single Market and the Customs Union without actually being in either, and without having to comply with free movement. It has long been understood that Brussels views this as ‘cherry picking’. What Mrs May's advisors may have underestimated is the legal conundrum.