Damp from next door

Other

Hi
A fellow landlord has the following problem.
His reliable tenant has recently left his terrace property but had not pointed out the damp which appears to be coming from the adjoining terrace house. The problem is the adjoining house has been derelict and in disrepair for some time and he has no way of tracing the owner. Thus repairing his damp problem would only be temporary if next door is not repaired also. The condition of the house next door is putting off prospective tenants. What is his best course of action?
1.To trace the owner, if possible?
2.Repairinf the damp
3.Can he get the local council involved?
Any advice welcome.