Bank of England Gov. Mark Carney has never shied away from doomsday Brexit warnings, but in his latest analysis he has gone further than ever.

While the BOE and the government both assume the economy could be as much as 11 percent smaller than if the U.K. remains in the European Union, the pace of the decline is far more rapid in the central bank's scenario. It also sees the pound in an unprecedented collapse to below parity with the U.S. dollar.

The dire assessments come before Prime Minister Theresa May's Brexit deal faces a key vote in Parliament next month. With the agreement facing criticism from all sides, there are doubts over her ability to get it passed, and she'll be hoping the stark analysis of a disorderly scenario may be enough to change some people's minds.