The Bank of England (BoE) confirmed Friday night it was secretly researching the financial risks of Britain leaving the EU after it "inadvertently" emailed to a national newspaper.
The email was missent to the Guardian by Jeremy Harrison, BoE's head of press.
The Guardian said the email indicated a small group of senior staff were to examine the economic effects of Britain leaving the EU under the authority of Sir Jon Cunliffe, who is the deputy director for financial stability.
According to the email, the press and most staff in BoE must be kept in the dark about the work underway.
A statement from the bank said: "Information related to planned confidential Bank work on the potential implications of a renegotiation and national referendum on the UK's membership of the European Union made its way into the public domain, due to an internal email sent inadvertently to an external party."
"It should not come as a surprise that the Bank is undertaking such work about a stated government policy. There are a range of economic and financial issues that arise in the context of the renegotiation and national referendum. It is one of the Bank's responsibilities to assess those that relate to its objectives," said the Bank.
"It is not sensible to talk about this work publicly, in advance. But as with work done prior to the Scottish referendum, we will disclose the details of such work at the appropriate time," said the Bank.
"While it is unfortunate that this information has entered the public domain in this way, the Bank will maintain this approach," the Bank added.