Labour members have committed the party to dissolving the independent sector if it wins power.
At the party’s conference in Brighton, shadow education secretary Angela Rayner said Labour’s first budget would strip private schools of their charitable status, subsidies and tax privileges.
A motion supported by delegates at the conference went further and called for funds, investments, properties and assets to be “redistributed” to other schools.
The motion also called for universities to be stripped of their autonomy and quotas imposed to mandate the number of privately educated students they could admit.
Ms Rayner said she would rename the Social Mobility Commission the Social Justice Commission and task the body with “integrating private schools” into the state sector, despite warnings that this would put strain on state schools.
Geoff Barton, leader of the ASCL head teachers’ union, warned the plan would cost the state sector £3.5bn and force it to absorb 600,000 extra pupils.
The move is “fuelled by ideology”, Julie Robinson, chief executive of the Independent Schools Council (ISC), said in a statement.
Robinson also warned the plan would breach the European Convention on Human Rights, which says that “the state shall respect the right of parents to ensure such education and teaching in conformity with their own religious and philosophical convictions”.
“Abolition would represent an act of national self-harm. Tearing down excellent schools does not improve our education system. The repercussions would be irreversible and far-reaching, damaging educational opportunities and limiting life chances,” Robinson said.
Mike Buchanan, executive director of the Headmasters’ and Headmistresses’ Conference (HMC) described the plan as an “act of unprecedented vandalism”.
“Any government has a duty of care to all its citizens and this would harm children in independent and state schools, harm families and harm freedom. It could cripple an already cash-strapped education system and cost rather than win Labour votes,” Buchanan said.
The motion passed would impose a 7% cap on independent school students at university, cutting the numbers from 140,000 to 98,000.
Diane Abbott, the shadow home secretary, was accused of hypocrisy because she sent her son to the fee-paying City of London School. She told Sky News: “As you well know, I sent my son to private school some years ago but if the party takes that position, I would support it. I did what I did, and I talked about it at the time and you can’t keep rehearsing those arguments.”
Shadow attorney general Shami Chakrabarti also privately educates her son who attends Dulwich College in south London.