Scotland will hold a new referendum on separation from the U.K. unless it can stay in the European Union single market, Nicola Sturgeon will warn this week, adding to the pressure on Theresa May as the U.K. prime minister draws up plans for Brexit. Scottish First Minister Sturgeon will detail proposals for a new arrangement with the U.K. to enable her country to remain inside the single market area after Brexit, even if the London government pulls England out. Voters in Scotland chose to stay in the EU in June’s referendum and now face being pulled out against their wishes by votes cast in England, she said in an commentary published in the Financial Times on Sunday. “It remains my view, and that of the government I lead, that the best option for Scotland remains full membership of the EU as an independent member state,” Sturgeon said. “Independence must remain an option for safeguarding our European status, if it becomes clear that our interests cannot be protected in any other way.” The ultimatum from Edinburgh on single-market membership will intensify the strain on May, who’s already battling to contain tensions within her own Conservative Party. On Sunday, Liam Fox, the international trade secretary, hinted that he was keen for a clean break from Brussels, while the former chancellor, George Osborne, warned that the U.K. should keep the closest possible ties to the bloc. May has promised to listen to the governments of Scotland, Wales and Northern Ireland before taking an agreed U.K.-wide negotiation position to Brussels for formal talks, due to begin by the end of March. Political Goodwill Sturgeon said she wanted the U.K. as a whole to remain inside the single market, with tariff-free trade and freedom for banks to provide services across the 28-member bloc. “If the U.K. government opts not to remain in the single market, our position is that Scotland should still be supported to do so—not instead of, but in addition to, free trade across the U.K.” she said. A policy paper will outline how such a radical step could be achieved, including which powers would need to be devolved from London to Edinburgh, she said, warning that 80,000 jobs would be lost if Scotland left the single market. Such a solution will require “political goodwill and an openness to new ways of doing things,” Sturgeon said. On Sunday, Fox warned that if the U.K. sought to remain part of the customs union—the EU’s tariff-sharing trade bloc—it would “limit” the country’s options for new trade deals. He told the BBC’s Andrew Marr show that Turkey could provide a hybrid model for partial membership of the customs union, adding that the U.K.’s future relations to the group didn’t have to be “binary.” In an interview on the same show, Osborne warned against ending tariff-free trade with Germany and France after Brexit. He said leaving the single market and the customs union would be the biggest act of protectionism in British history.