Four in five headteachers suffer abuse from pupils' parents, including physical assaults, spitting and trolling, survey finds

82% of school leaders said they had been abused by pupils' parents in the last year .

Abuse includes physical violence, verbal attacks, spitting and online trolling.

86% of respondents said parental abuse has increased in the past three years .

One victim said she had her face slapped and was "threatened with murder over the phone".