Children as young as seven are to be taught in schools to stop using the terms 'boys' and 'girls' – in case they discriminate against transgender pupils.

A guidebook for teachers, parents and pupils to be sent to schools around Britain advises against using language that suggests there are only two genders. It also condemns saying 'ladies' and 'gents'.

Instead the book – described as 'damaging' by critics – offers a bewildering array of alternative terms to describe gender and sexuality. Children who think of themselves as being the gender with which they were born are described as 'cisgender'. Other terms offered include 'panromantic', 'intersex' and 'genderqueer'.

Controversial: Children as young as seven are to be taught in schools to stop using the terms 'boys' and 'girls' – in case they discriminate against transgender pupils (stock photo)

The book – Can I Tell You About Gender Diversity? – also features the use of hormone blockers by a fictional 12-year-old 'transitioning' from female to male in order to stop the onset of puberty. The treatment is controversially available to children on the NHS, as first revealed by The Mail on Sunday.

Billed by the publishers as 'the first book to explain medical transitioning for children aged seven and above', it is distributed by Educate & Celebrate, a Government-funded body that goes into primary and secondary schools to give lessons on 'gender diversity'.

The organisation received £200,000 of taxpayer-funding from former Education Secretary Nicky Morgan and is endorsed by Ofsted. Earlier this year, the watchdog described as 'innovative and visionary' their work educating staff and children on gender and sexuality.

But politicians and leading religious figures last night lambasted the advice to stop saying boys and girls as 'damaging'.

The book follows Kit, a 12-year-old who is transitioning from female to male, and features illustrations that may appeal to young readers, including one of a 'gender-neutral' unicorn whose genitals are masked with a star. A key passage from the book advises that the use of 'boys' and 'girls' excludes transgender children – and reinforces the idea that there are behavioural differences between the sexes.

Former Tory Party chairman Lord Tebbit said: 'I think it is damaging to children to introduce uncertainty into their minds.'

A guidebook for teachers, parents and pupils to be sent to schools around Britain

Sir Anthony Seldon, the former Master of Wellington College, said: 'We have to respect the feelings of everybody, including teachers and parents who want traditional modes followed.'

And the Bishop of Chester, the Right Reverend Peter Forster, added: 'This is likely to sow more confusion than clarity.'

As an alternative to using the terms 'boys' or 'girls', the book by C.J. Atkinson – a poet, academic and 'trans advocate' – suggests: 'It may instead be preferable to group students into classes, or houses, or pupils.' In another part of the book, Kit talks about his fictional school, explaining that when children in his class were split into groups they were divided by numbers or heights. Kit says: 'This meant that when we were asked to do something, I didn't feel that I was weird or different.'

Other labels in the book include 'transman', which describes a man who was born female but who identifies as male; 'transwoman', which indicates the opposite; and 'panromantic' – someone who has a 'romantic attraction towards people of all gender identities'.

The book will be released by publishers Jessica Kingsley next month. Educate & Celebrate, which holds hundreds of workshops in schools, will send copies to the 120 'best practice' schools with which it works. It expects hundreds more head teachers to buy the book.