Open Question: insurance claim on a property i own?

i own a ground floor flat & the flat above had a leak in its bathroom bringing the ceiling down in my property,s bathroom . i a have had a couple of quotes for the repair work to be done but the landlord of the property above is refusing to pay for the repair work or go through is insurers what can ido? also , although the ceiling came down in the middle of the night , apart from two adults who live in the flat there is also two young children who could have been seriously hurt due to what i believe is down to poor maintenance of the above flat by the landlord, can i sue ?