The slash in value is thought to be a reflection of deteriorating investor sentiment towards the industry, according to a Sky News exclusive.
As part of the bank’s half-year results out tomorrow, it will reveal the 20% stake Co-Op Bank has is now valued in the region of £145m, down from £224m in April this year.
The former mutual warned earlier in the year that an uncertain market birthed from the Brexit result is likely to damage mortgage growth.
The writedown in value is expected to contribute to an overall drop in profits after the bank made a loss of £177m in the first half of 2016.
Despite expenditure on other projects, insiders have said that borrowing has remained stable.
Co-Op’s food retailing business has performed strongly as the company aims to rebuild the loyalty of its members during these turbulent times as a new membership proposition goes live.