I agree with kurnal, in this instance the householder has no duty of care to alert the neighbour and the housing provider is correct. A major problem would arise if the housing provider had told the householder to alert the neighbour, in which case if anything happened to the householder whilst they were carrying out this function the housing provider could be subject to litigation. What training did the householder receive to ensure they were safe to carry out this function etc. I was involved in a litigation case where an employee who was office based and spent his day pushing a computer mouse about a desk decided he would help an outside contractor load a lorry and injured himself then he sued the firm. The questions that came from the legal firm included was he risk assessed to carry out this role, had he received manual handling training to lift this load etc. etc.
Following this the housing provider is correct, however this would not prevent the householder alerting the neighbour if they so desired as a 'good citizen'.
From another angle if I was carrying out an FRA on the premises and I was told that the procedure for the evacuation of a disabled person was for a neighbour, who is not an employee and over whom the housing provider has no control, to come in, alert the disabled person and assist that person to leave. I would immediately record that this procedure is totally inadequate.