Goodmorning I see you have been waiting for an answer. I am sorry for that.
If there is no building control paperwork. I would get in touch with the local Planning Office. Explain your situation and concerns. I expect they would send a surveyor in order to make sure there are RSJ's or other supports correctly in place to stabilise the upper walls. If not the other party would I believe be liable and have to arrange for that work to be remedied. I cannot confirm that but the Local Planning Officer would be able to.
I hope you get some answers to your concerns