Best-selling author Juno Dawson has claimed a school cancelled her event because she is transgender.

Dawson, a teen novelist who is best known for This book is gay and Mind your head, was due to talk about her new book Margo & Me at Brownedge St Mary’s Catholic High School in Preston on Wednesday.

But the author claimed she was informed with just 48 hours notice that the event had been cancelled. She said a member of school staff told a representative of the company organising the talk that it had been considered “inappropriate” and the “subject matter” meant “they didn’t think it was suitable”.

The school, which has been applauded for its work on LGBT rights, denied the visit had been cancelled, instead insisting it had simply been postponed. However, the novelist has insisted no one has been in touch with her to reschedule and attempts to arrange something were rejected.

Dawson, who came out as transgender in 2015, argued there was nothing inappropriate about the book for an audience of school pupils. The novel is written for people in their early teens and explores a grandmother and granddaughter in South Wales during World War II.

“It’s a perfectly appropriate book for that audience,” Dawson told BuzzFeed News. “All week I’ve been speaking to year sevens and eights with no problems – in a mixture of grammar schools, private schools, faith schools, all sorts of different schools.”

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She said she was shocked her visit had been cancelled, saying: “I went through stages – the first was I felt personally attacked and quite mortified. But then I became angry as I very quickly realised that you can’t do that – you can’t discriminate against people on the basis of their gender.”

“There will be young people at Brownedge who will be LGBT. Those kids knew I was coming and now I’m not. It beggars belief. One does wonder what kind of support those kids are getting.”

She tweeted: “I’m so cross. The LGBTA students @BrownedgeStMary knew I was coming and now that I’m not. What message does that send them? Fuming.”

The talk had been widely promoted, with posters in the library and notes to parents. “We can’t wait to welcome you to our school and hear about your new book, #MargotandMe,” the school said in what appears to be a since-deleted tweet.

The head-teacher of the school told the publication the event had not been cancelled and outrightly denied the allegation of discrimination.

“I asked for the visit to be postponed to a later date not cancelled,” he said in a statement. “The postponement of Juno’s visit was not due to the fact that Juno Dawson is transgender … We would never discriminate against any individual on the grounds of sexual orientation or gender identity as we teach our children that each individual person is precious and unique.”

“A representative said she felt the subject matter meant that a visit was inappropriate at this time because we wanted a proper context for it so that our younger students could get more value out of it …,” he added. “We wanted more time to do this theme justice for our younger students.”