Legal advice

Hey everyone, I was wondering who in the uni i can talk to about legal advice..

Basically my flat is fully infested with mould (this was here before we moved in in july, theres evidence in the inventory for multiple rooms). We emailed the agency about it in August to no reply, and then more recently a few weeks ago to which we got a response. I have no faith that the landlord will fix the problem (he is only just coming out tomorrow to look at it) as in the past before we moved in, mould has just been painted over.

We are having to move out due it affecting our health so badly and have thankfully secured a flat. The problem is that we would have to pay double rent for the month of December, which we cannot afford. Is there anyone here who knows if we can withhold rent? Or who to go to about this (e.g. student union or the law department)?

Thanks!