a high-profile grammar school threatened with takeover by the Church of England has three weeks to fight for its independence. The Liverpool Blue Coat school is challenging a claim that an old document linked to its founding means it should be reclassified as a church school.

Lawyers have until February 9 to make their case to the Department for Education and Skills, following a comment by Alan Johnson, the Education Secretary, that he was “minded” to grant the reclassification.

Since the Church first staked its claim at the end of 2004, it has met with fierce opposition from Blue Coat supporters, who fear the school will be forced to change its ethos and admissions policy.

Sandy Tittershill, the headmaster, said: “I have had almost 1,000 letters of support from people who want the school to remain as it is. We are unwilling to become a church school. We think it is absurd and unreasonable. Anyone with half a brain would say so.”

Mr Tittershill, who has been at the school for 41 years, said there was no relationship between the church and the school to justify it being reclassified. “If the Bishop of Liverpool bumped into me in the street, he would not know who I was,” he said. “The Church has never been visible at the school.”

The claim stems from a charter discovered by officials in the diocese of Liverpool, which states that the school should teach religious education “in accordance with the doctrines of the Church of England”. After the school refused its request to become a church school, the diocese took its case to the DfES.

“The issue is down to a statutory definition and it is the Secretary of State’s decision,” said a CofE spokesman. “It is clearly important for the future of schools that they are correctly classified and know where they stand.”

There are 4,500 CofE primary schools - one in four of the total - and 230 secondaries, but a further 74 are in the pipeline.

The academically selective Blue Coat school is non-denominational, attracting pupils from a variety of faiths. The diocese said it would not interfere in the running of the school, by appointing governors or changing its admissions code.

But Mr Tittershill was concerned the school would be forced to fall into line with other church schools in Liverpool, which give priority to pupils based on faith.

“One of the major strengths of the school is its diversity,” he said.

“Liverpool needs the Blue Coat school as it is, a multicultural, dynamic and tolerant community.”

Mr Tittershill said the school would seek a judicial review if the DfES decision went against them.