The head of a group of 600 private schools has hit out at the “truly toxic portrayal”, in the wake of Labour endorsing a series of measures that would effectively abolish them.

Christopher King, the chief executive of the Independent Association of Prep Schools (IAPS), was due to tell his organisation’s annual conference on Thursday that private schools offered a “premium product” for pupils, without the rote learning and changes inflicted by the previous education secretary Michael Gove on state schools in England.

He also claims that private schools survive because they are better at providing a “holistic education” , and urges the government to issue education vouchers for parents to spend on school fees.

His defence of private schools follows a vote at the Labour conference on Sunday, when the party adopted new manifesto policies that would strip them of charitable status, add VAT to fees, restrict their pupils’ access to higher education, and redistribute their endowments, investments and properties to the state sector.

In his speech to prep school heads and governors, King attacked the “truly toxic portrayal” of private schools as being aloof from their community. He also accused critics of the sector of being hypocrites for allowing “selection by postcode and house price”, when parents buy expensive houses close to leading state schools.

Play Video 7:03 Should we abolish private schools? – video

“For me, that smacks of hypocrisy. How can these people attack parents for paying for their children’s education when they are doing exactly the same thing but via a different route?” King said.

“Social mobility, or the lack of it, is a major problem in this country. The easy cheap shot is to blame us who educate no more than 12% of the nation’s children. Really?

“Visit a typical independent school classroom with children of any age and you will see a more ethnically diverse group of faces looking back at you than is likely to be the case elsewhere.”

However, the headteacher of a state primary school in the south-east of England, speaking anonymously, rejected that claim, saying: “Any state school is more diverse in terms of backgrounds and incomes than the most diverse prep school, even in the wealthiest areas. Prep schools usually offer no bursaries or financial scholarships, they are worse in that respect than public schools.”

King’s organisation represents 600 prep and junior schools in England with around 160,000 pupils, educating children up to the age of 13. According to the Independent Schools Council, the average annual fee is just over £13,000 a year for day pupils.

In his defence of the sector, he was due to say: “There is no denying we offer a premium product and there is a cost for this but in turn it produces results.

“There are regional differences, but the state per-pupil primary-age funding level is circa £5,000. The comparable figure for independent schools is two and a half times this. What does this extra per-pupil funding bring apart from excellent facilities? More, specialist teachers from an early age, smaller class sizes and a commitment to the development of the individual.”

He contrasts the “Michael Gove-directed changes focused on the rote and robotic” in state schools with the autonomy enjoyed by private school heads, “free of the shackles of government ministers’ diktat”.

Head of Eton hits back at Labour plans to abolish private schools Read more

“It is a simple truth that one of the great joys, and indeed responsibilities of being a head in an independent school is that you get the freedom to choose the curriculum and co-curricular shape that is best for the pupils in the school.”

The National Association of Head Teachers said all heads faced restrictions on what they could do and teach.

“In almost every case, whether you’re in the state sector or elsewhere, the headteacher’s office comes equipped not just with a desk and chair but a straitjacket too,” the NAHT said in response to King’s speech.

“Accountability, funding, data and problems with recruitment – all well known in the state sector – all act against school leaders who want to use the freedom and autonomy that come with the role. In the independent sector, there are different problems.

“Good leadership is about having a clear plan to overcome whatever obstacles you face in a way that works for you, your school and its pupils.”