The bosses of several of America’s biggest banks and corporations have warned Theresa May they will pre-emptively shift operations into Europe unless she can provide early clarity on the future shape of EU-UK relations, The Telegraph has learned.

The ultimatum was delivered at a round-table meeting with Mrs May in New York this week attended by a host of key US investors, including major City investors such as Goldman Sachs, Morgan Stanley and BlackRock.

According to an account of the meeting obtained by The Telegraph, Mrs May declined to provide information about how the British government would approach the Brexit negotiations, other than pursuing a deal that was “in the national interest”.