Party Wall and Damp at First Floor level

Part of the first floor bathroom wall is damp (but nowhere near the bath, shower or water pipes/sources). I believe the damp is coming through the party wall from the neighbour\'s bathroom - their shower and bath is the other side from my damp patch. I have contacted the neighbour, shown them the problem and they appear not to have looked at a remedy/think it\'s their problem. They are not answering my emails. I have registered a claim with my insurers but there is no point undertaking remedial work until the damp source is rectified. Any suggestions as to my next step?