A secret Treasury document detailing the government's no deal contingency planning, under the code name Operation Yellowhammer, warns of the importance in maintaining confidence "particularly... for financial services".
The document, which was snapped by political photographer Steve Back being carried by City minister John Glen into a Whitehall meeting this morning, included a series of discussion points for how the government will mitigate "the immediate impacts of a no deal Brexit".
Key Treasury objectives in the document include the importance of building a "communications architecture that can help maintain confidence" if contingency plans are triggered. This was said to be particularly important for financial services.
It also raises the question of "rail access to the EU" and the cost of Yellowhammer, with suggestions that departments should look to fund the no deal planning from "internal reprioritisation".
The Treasury has put £1.5bn-worth of funding aside for a no deal scenario, although it is understood that none of this money has yet been spent.
Asked about the leak during a visit to Glasgow, chancellor Philip Hammond said: "Departments have the funding for no-deal planning. What we’re beginning to discuss is now part of long term contingency planning.
"In no deal circumstances we would have to refocus government priorities so that government was concentrated on the circumstances that we found ourselves in. Let me reiterate again that is not the outcome we are expecting and it’s not the outcome we’re seeking."
The document also notes that the Civil Contingencies Secretariat - a Cabinet Office department charged with emergency planning against disruptive challenges - held a two-day workshop last week to review the Treasury's "plans, assumptions, interdependencies and next steps".
Yesterday during PMQs, Theresa May insisted that a no deal would not be "the end of the world".
A yellowhammer is a bird, whose song sounds "a little bit of bread and no cheese", according to children's author Enid Blyton.