The Principal of Queen's College in London has accused Chancellor Rachel Reeves of damaging female equality and opportunities after her private school fees VAT hike.
Richard Tillett's letter to the Times told how one private school within an hour of the Chancellor's own constituency has been forced to accept boys to a previously girls only school from September 2026.
According to the principal, Wakefield Girls' High School is soon to start welcoming boys almost 150 years after it was founded in 1878.
Mr Tillett added that another local school, Harrogate College, had taken the same decision, while a third, Queen Margaret's School in York, is closing its doors altogether.
Writing in the Times, he said: 'All-girls' education matters, and the state does not do enough to provide it.
'Girls' schools regularly dominate the top of the national league tables, and all the evidence shows that, if girls are educated separately from boys, they achieve more highly, do more science, participate in more sport and have greater levels of self-confidence.
'Also last Friday the High Court judged that the imposition of VAT on school fees was legal.
'Whether it is moral is a different story. When will the Chancellor, who went to an all-girls' school, realise the damage that her policy is doing to the female equality agenda?'
Richard Tillett's letter to the Times told how one private school within an hour of the Chancellor's own constituency has been forced to accept boys to a previously girls only school from September 2026
Queen Margaret's School in York is closing in July after 125 years of privately education girls
Mr Tillett, who himself attended a private school before going on to study at the University of Cambridge, had his comments on the Times' letter page.
Queen Margaret's in York told parents last week it would be closing after 125 years of providing education for girls aged 11 to 18.
Labour's introduction of VAT on school fees, as well as "increased national insurance and pension contributions, the removal of charitable-status business rates relief, and rising costs for the upkeep and operation of our estate", were all behind the closure, a statement from the school said.
Chair of the Board of governors Terry Burt said there were simply not enough children enrolled in September to continue operating past the end of term, and the school will close on July 5.
A notice to appoint an administrator has been filed with Companies House.
The Labour government moved quickly after winning last year's election to introduce VAT on private schools fees, which had previously been exempt from the tax - essentially hiking fees by 20 percent.
They were warned this could price middle class families out of the market, but a High Court ruling this week ruled in Starmer's favour.
The judicial review claim, heard earlier this year, aimed to have the 20 per cent tax declared 'incompatible' with human rights law.
Wakefield Girls High School, around an hour from Rachel Reeves' constituency, is to accept boys from September 2026
However, in a decision handed down on Friday, judges rejected all claims, despite agreeing with some of the arguments.
The controversial tax, pledged in Labour's manifesto, came into force in January this year.
Three groups of families - most of whom are anonymous - joined private schools in bringing a legal challenge against the policy.
Their lawyers argued the tax is a breach of children's right to an education under the European Convention on Human Rights (ECHR).
The various families also said it was 'discriminatory' - either because their child has special educational needs (SEN), has a preference for a religious education, or because they need an all-girls environment.
But Dame Victoria Sharp, Lord Justice Newey and Mr Justice Chamberlain concluded the VAT policy was 'proportionate' in its aim to raise extra revenue for state schools.
They added Parliament ultimately had the right make the decision.
A government spokesperson said: 'Ending tax breaks for private schools will raise £1.8bn a year, helping to support public services including the 94% of pupils who attend state schools.'