The co-op doesn't have shareholders in the strict sense, it has members which is different. How closely the co-op bank is actually related to the rest of the organisation I couldn't say. To be fair, the co-op *as an organisation* does have a set of rules it's supposed to adhere to in it's corporate 'charter'. If the banking part has failed to do that the rest of the board may well follow the CEO out the door.
If you're a 'household customer' with the bank your cash is legally protected (unless you've got an awful lot of it) but if they do crash having played fast & loose it could fatally damage the entire brand, which very much sells itself as being a more responsible and ethical option.
FWIW JJ, I'm a Smile customer so I'm in the same boat as you, whatever boat that may turn out to be.
Jon