The Co-op Bank is putting itself up for sale, inviting offers to buy all shares.
The bank, which nearly collapsed in 2013, is 20% owned by the Co-operative Group and has four million customers.
It was bailed out by American hedge funds but has been unable to strengthen its financial position because of low interest rates.
Bank chairman Dennis Holt said: “Customers value the Co-operative Bank and our ethical brand is a point of difference that sets us apart in the market.
“While our plan has been impacted by lower for longer interest rates, the costs associated with the sheer scale of the transformation and the legacy issues we faced in 2013, there is considerable potential to build the bank’s retail franchise further using the strength of the brand, its reputation for strong customer service and distinctive ethical position.”