The flat above mine is leaking water into my bathroom causing damage to my ceiling and walls. The tenants of the flat above know it leaks

but have done nothing to correct the problem nor supplied me with contact details for the leaseholder who ownes the flat. I am also a leaseholder (the block is owned by Wandsworth Council) and want to rent my flat out too; but I cannot do this until the leak has been fixed.

The council claims it has contacted the leaseholder and been assured the leak has been fixed but water ingress is still causing damage to my flat. What options to I have to resolve this situation?