The Bank of England was forced on Friday night to confirm that it was secretly researching the financial impact of a possible decision by Britain to leave the EU, after it mistakenly emailed a journalist with the details.
The confidential email, mis-sent to the Guardian newspaper, is reported to include details of the study, dubbed "Project Bookend". It also stated that the press and most staff at the BoE should be kept in the dark about the work under way.
The decision by the central bank comes only weeks after the Conservative party secured a majority in the UK general election, paving the way for a referendum by 2017 on British membership of the EU.
On Friday, David Cameron began discussing with European partners how to renegotiate the position of the UK in the EU in advance of the referendum.
The BoE issued a statement responding to the revelation, saying it was entitled as a regulator to conduct studies over possible financial shocks that could hit the UK.
"It should not come as a surprise that the bank is undertaking such work about a stated government policy," it said. "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."
According to the Guardian, the email was sent by the private secretary of Sir Jon Cunliffe, the BoE's deputy governor for financial stability, to four senior executives, and then mistakenly forwarded by Jeremy Harrison, the bank's head of press, to a journalist.
The revelation will raise questions over whether it is appropriate for the BoE to undertake such studies in secret. Mark Carney, the central bank's governor, took steps last December to increase transparency within Threadneedle Street, promising to publish voting details and minutes of interest rate decisions at the time they were announced.
"These changes will enhance our transparency and make us more accountable to the British people," Mr Carney said then.
However, the bank has now insisted that it is right to hold such studies secretly, drawing analogies with work done ahead of last year's referendum on Scottish independence. It said: "It is not sensible to talk about this work publicly, in advance. But as with work done before the Scottish referendum, we will disclose the details of such work at the appropriate time."
The BoE confirmed that it would be looking into its processes in light of the incident.