Our local council, and the police, have said that statements and updates will be posted via next door. However it's a very one way conversation. The only way the police or council see what you say is by replying to them. I'm sure they have fake accounts where they can see what people post in neighbourhood groups, but it seems very inefficient. I should test it, by offering to sell drugs on Next door, and see if the police come knocking. I don't know what I can do to upset the council as a test, maybe offer to sign off planning applications without any official capacity.
This is the header to local police's nextdoor page
"Hammersmith & Fulham Police
252 Uxbridge Rd, London
We endeavour to check in here as often as possible, but do not report crime here. Nextdoor does not allow us to view residents posts. "
The council
"Your local public services on Nextdoor
Nextdoor also provides a platform for local public services. H&F Council, the local police, Sobus (the community development agency) and a number of other organisations have all signed up to keep you in touch, get feedback from you, and help us to work with you better. Public services cannot see anything that you post on your neighbourhood site – that is completely private for you and your neighbours."