It seems there's currently another director who could use the available legal mechanisms to take over from the missing director-CEO but is not doing so, and previously a board that resigned rather than use the available legal mechanisms (which would be easier for a group of them). The organisation is a CIC, which means it is regulated, and has a constitution whereby a non-responsive director-CEO can be removed, and indeed places a duty on the other directors to do so if that's what it takes, which they haven't done.

It is possible that the rest of the board was derelict in their legal duties by resigning if they knew what the consequences would be.

Even if there are no directors left, or only an unresponsive one, the collective owners of the organisation have a right to get together and install a new one, and there are legal mechanisms to do that if there's no director or secretary to do the administration in the usual way.

The keys to the bank account will be provided to the other director or new directors if they show to the bank's satisfaction that they have the right to them.