The Royal School in Haslemere is to close in the summer after almost two centuries.
The private school, which was founded in 1840, announced on its website that it would close on August 31, 2025.
United Learning, which took over the school in 2019, said it had invested over £16 million to address historic debt and subsidise losses but was unable to reverse the decline in demand.
A spokesperson said: “When the governors approached United Learning in 2019, the school was in serious financial difficulty and heading towards closure.
“Since then, we have made strenuous efforts to overcome these systemic issues and spent over £16 million in addressing its historic debt and subsidising the school’s ongoing losses, whilst conducting extensive marketing to secure a turnaround in demand for places.
“Despite everyone’s best efforts, however, demand has not risen as hoped; for a school with places for 350 pupils, the roll in September was projected to be fewer than 100.
“The financial support required to continue subsidising the school has grown to an unsustainable level and further reductions in pupil numbers would, we believe, increasingly risk compromising the educational experience of pupils.
“We have therefore taken the sad decision to close the school and will be doing whatever we can to support pupils and staff in finding new roles and school places, including where possible within our group.”
Greg Stafford, the MP for Farnham and Bordon, said he was “deeply saddened” by the news of the closure.
“This is devastating news for the current pupils and their families, who now face the difficult task of finding new schools,” he said.
“This will be especially challenging for those on bursaries and scholarships, which may not be available elsewhere.
“Many current and former pupils and staff have contacted me today to express their shock and sadness at the loss of a school with such a proud history, dating back to 1840 as the Royal Naval School.”
He blamed Labour’s taxation on private schools for the closure.
"This closure is yet more proof that Labour’s reckless policies are wreaking havoc on our education system,” he said.
“Their punishing tax on private education and their relentless drive to increase costs, including higher national insurance contributions, are making it impossible for smaller independent schools to survive.
“Labour claimed the impact would be minimal, yet we are now seeing the reality: pupil numbers are falling, schools are closing, and families are being forced into an overstretched state sector that does not have the space to take them.”
The closure of The Royal School follows that of Alton School, another private school, last year.
“Labour’s policies are wiping historic schools off the map and will end up costing taxpayers even more in the long run,” added Mr Stafford.
The Royal School, a private day and boarding school for boys and girls aged 10 to 18, was originally established as the Royal Naval School in 1840 to educate the daughters of navy and marine officers.
The school charges £6,552 per term for day pupils in Years 7 to 13 and £13,398 per term for boarders.
HRH Anne, the Princess Royal, is the official president of the school.