Water damage from upstairs flat - health risk

Hi there
I own a flat on a long lease and the freeholder lets the flat upstairs (two flat maisonette). I had my daughter's room redecorated and discovered alarming damp and mould - black, wet, over the entire wall - horrid. It has been addressed ie dried out and treated), but the bathroom upstairs still has leak issues - the shower has no shower curtain and water splashes direct onto the wall (no tiles, or special coating) and is very damp. This is the wall the descends to my daughters room, and the water is soaking down. There is also a leak from the radiator and I can see the damage this is causing to my flat.

The tenants upstairs have tried to get the landlord/freeholder to tile the bathroom properly and fix the radiator, but he keeps putting it off.

If he doesn't get the bathroom water tight, my daughter's room will get mouldy again - which is a health risk - as well as meaning I have to do the decorating again! It's not nice for the tenants too!

Could someone tell me what his obligations are on this, and whether I can go through our insurers?

I have sent him an email and pictures, but he has not responded.

Many thanks for reading