The director of the Christian Institute has accused Ofsted and the Department for Education (DfE) of giving "inadequate attention" to the bullying of Christian children in Muslim-majority schools in Birmingham.

In a letter reported by the Daily Telegraph, Colin Hart wrote to education secretary Nicky Morgan about the so-called 'Trojan Horse' scandal, involving a group of Birmingham schools said to have been targeted for control by hard-line Muslim activists.

Hart said that it was "striking" that while official reports into the scandal listed examples of anti-Christian intolerance in the schools involved, "none of these are noted in the Ofsted reports on those schools".

Mr Hart wrote: "You will see they include anti-Christian chanting in assemblies, GCSE pupils who opted to learn Christianity being left to teach themselves, and Christians being called 'ignorant' or 'liars' by teachers."

He added that it was disturbing that there was "a complete lack of any specific plans of action to tackle anti-Christian intolerance".

Hart said: "Ofsted's system for detecting intolerance is clearly inadequate if it is not picking up on anti-Christian sentiment. In fact, Ofsted may be part of the problem."

He criticised what he argued was an inappropriate focus on gay marriage, saying: "Whilst guidance from your department says there is no obligation on schools to promote gay marriage, there have been Ofsted inspections in several parts of the country where Ofsted inspectors have implied, via questioning of pupils, that they ought to accept gay marriage.

"We are aware of several cases of this approach being taken with primary age pupils, some as young as six."

An Ofsted spokesman said: "Ofsted deplores bullying in all its forms. We expect schools to promote British values including mutual respect and tolerance of those with different faiths and beliefs.

"However, it is nonsense to suggest that an Ofsted inspector would expect a school to have taught six year old pupils about same sex marriage."

A DfE spokesman said: "Bullying of any kind is unacceptable and all schools should take an active role in tackling it. Heads, teachers, governors and trustees are working tirelessly to resolve deep seated issues at these Birmingham schools which developed over a long period of time."