Headteachers will debate whether Education Secretary Nadhim Zahawi should intervene at a Catholic school where a visit by a gay author was cancelled by the archdiocese.

Simon James Green, a young adult author, had been invited to discuss his books as part of World Book Day at the John Fisher School in Sutton, south London, in March before the Archdiocese of Southwark got involved days beforehand and the event was cancelled.

The diocese also intervened to remove several governors supporting the school’s leadership team, who wanted the visit to go ahead.

An Ofsted monitoring report published on Wednesday said the archdiocese’s decision to impose an interim executive board (IEB) after suspending the governing body – which voted to back the school leaders’ decision not to cancel the visit – was “made unilaterally and without due regard to the published statutory guidance”.

On Thursday, staff members of the National Education Union at the school went on strike over the issue.

The NAHT school leaders’ union will debate whether Mr Zahawi should investigate attempts by the archdiocese to appoint governors who are “riding roughshod over existing statutory guidance”.

An emergency motion at the NAHT’s annual conference in Telford on Saturday will call for heads to send their “support and backing” to the senior leadership of the school and its governors “who have stood firm in their determination to recognise, value and celebrate the rights and the lives of the young LGBT+ people in their community”.

It will also call on the NAHT to “ensure that the Secretary of State for Education investigates the removal of foundation governors at the school” as well as the “continued attempts by the archdiocese to appoint governors who are riding roughshod over existing statutory guidance setting out the arrangements for the constitution of governing bodies”.

Rob Kelsall, national secretary of the NAHT, who has written to the Archbishop of Southwark about the “disturbing developments” at the school, told the PA news agency that “one of the foundation governors attempted to appoint himself as chair of governors over and above the properly elected chair of governors”.

“So we’ve now got the most ridiculous situation where you’ve essentially got two people claiming to be the chair of governors, which is causing utter confusion and destabilising for the entire school’s community.”

He said he had visited the school on Wednesday and that “in front of our very eyes, the behaviour that was being displayed was one that was extremely hostile”, adding that it appeared “sexist in regard to shouting down and talking over the person who is recognised by the school’s community as the chair of governors, and an adviser to the governing body, both females – and people had to be rebuked for that”.

“I have to say that in all my years I’ve never experienced such hostility demonstrated in front of our eyes and in a professional environment. They were being verbally attacked, and talked down to, talked over,” he said.

He added that it was a shame that a meeting intended to avert strike action “was actually consumed by in a way that felt deliberate and more focused on a power struggle between the diocese-appointed governors seeking to take control”.

He said he did not see “any prospect” of the situation being resolved amicably, and that the appointment of new foundation governors had taken the situation “from bad to worse”.

He said: “This isn’t a time for people to sit on the sidelines – we’ve got to protect the outstanding education of those young people, we’ve got to protect the leadership of this outstanding school.

“Ofsted have said in their report that immediate steps must be taken to restore stability to governance at the school. The diocese need to take urgent steps to remove the foundation governors which they have appointed. There’s no time to waste.”

A statement from the Archdiocese of Southwark said: “As with all Catholic schools, The John Fisher School is a welcoming and inclusive place for all pupils, and we were extremely pleased that this was recognised by Ofsted.

“The Archdiocese of Southwark was concerned however, that there were inaccuracies in the report surrounding the cancelled visit of Mr Green, with evidence appearing to be drawn solely from media reports. The Diocesan Education Commission has today written to Ofsted asking them to review the report again.

“Respect for the God-given dignity of each human life sits at the heart of Catholic education and respect is a two-way street.

“Literature that insults the faith, which in the case of Mr Green’s book was a highly sexualised re-writing of the Lord’s Prayer, understandably causes offence to many Christians, and as such has no place in a Catholic school.”

In Mr Green’s young adult novel, Noah Can’t Even, school bullies create a homophobic rendition of the Lord’s Prayer after Noah kisses his friend Harry.

An agent at Scholastic which publishes the book said: “The Lord’s Prayer scene in Noah Can’t Even has to be considered with the context of the whole story – this is a scene of homophobic bullying with an antagonist in the story using replacement words to abuse the central character, Noah. It is made obvious in the book that this behaviour is not acceptable.”