Hello
I had a council property temporarily a few years ago and the having animals was permitted, but they were limited. For instance you werent allowed to become a cat hoarder or anything
but i think that is also to maintain the standard of the property and as you've probably seen on TV the costs the council inccurs to clean and empty these places and usually the rehoming of 100 cats
However, my property was in England. My mother rents a council flat (ground floor, but only one flat above) in Scotland and she had her cat at the time. He has sadly passed and she now has 2 small dogs. I know she wouldnt of needed to report to the council about the dogs as her tenancy is existing (as would your friends be) but they were aware of the cat when she signed the agreement.
I think as a responsible cat owner, other tenants probably wouldnt even know your little un was there
the one thing that causes complaints from others would be noise or smell coming from the flat (these apply to anyone not just pet owners lol)
Personally, i dont think there would be a problem. Housing Association Houses have different rules and are stricter but Councils are much more accomodating.
I think a quick check of your friends tenancy agreement should do it and of course the usual safety thing with regards to balconys, but i think it'll be fine
I hope it goes well! Its hard especially when you just need somewhere until your on your feet and up and running, hope it works out