Behind the toilet boxing, damp, mold, a mess.

Hi, I hope someone can help? We’ve moved into a new house and the plumbing has been terrible. Everything leaks! We recently removed the toilet boxing due to all the floor being rotten through due to a leaking sink. Behind the boxing we found damp issues too. Can anyone help me pin point what actually needs fixing? Does the pipes need redoing, the drain sealing in to floor, the gaps where the wall meets floor filled, can condensation off the pipes cause issues? I look at what is behind the boxing and it just looks like a mess. Maybe it’s normal?

Photos of the issue. Thanks for checking it out.

Wow, that is certainly a strange setup.
Very crudely done.
Especially that connection made with a giant blob of caulk.

What country are you in?

Hi Jeff, sorry for slow reply. I’m in the UK