JK Rowling has condemned as “utterly shameful” the treatment of a teenage girl who felt forced to leave her school after pupils hounded her for challenging the views of a visiting speaker.

The author waded into the row after a teacher at the school claimed the unnamed girl was treated like a heretic for questioning a politician’s assertions about sex.

After debating with the speaker, a female member of the House of Lords, the sixth form student at the private girl’s school said she was surrounded by up to 60 pupils who shouted, screamed and spat at her. She escaped and said she collapsed, unable to breathe properly.

Teachers were initially supportive but withdrew their backing after the other sixth-formers accused the girl of ‘transphobia’, and the school ended up apologising for not maintaining a “safe space” in the sixth form.

The teenager returned to school a few times but was told she would have to work in the library if she said anything provocative in lessons, and faced bullying and accusations of transphobia from pupils throughout the school. She also spent break and lunch times in the library. The girl left in December and is studying at home.