Labour plans to integrate private schools into the state sector will result in larger classes and burgeoning costs, the head of a group representing Britain’s leading independent schools has said.

Fiona Boulton, the chair of the Headmasters’ and Headmistresses’ Conference (HMC), said that Labour’s pledge last week to endorse a series of measures that will effectively abolish private schools was based on “ignorance and the desire to damage”.

Boulton was due to address about 300 heads from many of the country’s most expensive independent schools at the HMC autumn conference in London on Monday as the battle over the future of Britain’s private schools gathers momentum.

Last week, the Labour party voted in favour of new policies that would strip private schools 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.

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In her speech, Boulton claimed Labour’s manifesto commitment was a vote loser and called on members to “fight alongside each other in pursuit of a privileged childhood for all”, adding: “We stand proud of our contribution to education in this country.

“This is a time for inclusion, acceptance and friendship and a time to inspire harmony. Voters want the government to help more children to get access to independent schools. Parents are ambitious for their children and people want to see our schools opening up, not closing down.”

Speaking on the BBC’s Andrew Marr show on Sunday, the shadow education secretary, Angela Rayner, argued private schools had been subsidised by taxpayers for far too long.

“I want a comprehensive state education system and I want to stop subsidising private education which is elitist, which entitles 7% of the population to do better than the rest at the expense of everybody else. We have to invest on everyone’s education.”

The HMC, whose members include the likes of Eton college, Westminster school and Wellington college, also published the results of a ComRes survey of 2,000 adults into attitudes towards Labour’s policy announcement.

Asked about whether parents should be able to choose to pay for their children’s education if they could afford it, two-thirds (68%) agreed, while 18% disagreed. The strongest support came from Conservative voters, of which 83% agreed, compared with 56% of Labour voters and 70% of Lib Dem voters.

Respondents were also asked whether they supported or opposed government policy to help pay for children from low income backgrounds to attend independent schools. Nearly half were in support and 27% opposed.

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

Boulton, who is also the head of Guildford high school, said: “As leaders of independent schools we need to keep listening and learning. But it seems that independence and choice are concepts which never go out of fashion.

“And do not be fooled into thinking that imposing crippling taxes is anything other than abolition by the back door. It would ensure that many independent schools would not survive and others will become more expensive. State schools will see larger class sizes and burgeoning costs.

“The decision taken by Labour to abolish our schools was based on ignorance and the desire to damage, whilst independent schools have for years been quietly educating children, alongside creating free and discounted places, sponsoring successful academies and delivering more than 5,000 helpful projects in state schools communities.”

A Labour source said: “Of course the establishment will try to defend its privileges. But these are leading questions that don’t tackle the real issues at all. We note that the private schools lobby failed to ask the British public whether they thought it was right that children’s life chances are determined by how wealthy their family is, or whether it is right that private schools don’t pay their taxes like the rest of us.”