I don't think the Co-op did anything wrong. I am so sorry you had that experience though. I can see how it happened despite your best efforts to plan and why it felt so humiliating. I know it won't take any of the shame away, but remember, you are pregnant. There is a reason why it happened. Another woman in the same stage of pregnancy with a baby that moved would have likely had the same thing happen. It's just one of those awful things about being female. I know why you feel embarrassed and TBH, I would feel that way too, but that doesn't mean we should feel embarrassed! Your body is working hard to grow and keep a baby safe. If things like this happen from time to time, it's just part of the package.
I do think it's wrong that there are so few public toilets available. Everyone deserves the dignity of being able to go to the toilet when they need it. I also think certain businesses should always have a public toilet available - if it was a big enough supermarket rather than a corner shop, I think it should have had one.
However, having seen the state of some toilets, I do sympathise with people who don't want to give access to all and sundry... I don't understand why so much of the general population thinks it's OK to leave toilets in such a grim state when they are well enough to clean up after themselves.
I don't know what the solution is.
There are plenty of public toilets in Europe, but you have to pay for them (which I resent).
I've never been to Japan, but I hear from friends that their toilets are always clean, and plentiful. I wish we had that. How can we build more toilets, open up more toilets, and convince people to not abuse them so we can continue to have nice things?