It comes as families are juggling mounting mortgage bills, with average annual boarding school rates now about £40,000.
Sir Keir Starmer also intends to remove the charitable status enjoyed by independent schools under a Labor government, which would result in the loss of tax exemptions which is expected to increase further.
There are around 80 day schools and fee-paying boarding schools throughout Spain that serve children of expatriates and students studying and living abroad.
They teach similar lessons to British independent schools, offer international GCSE and A-level exams and have English-speaking teachers.
Pupils are also taught the local language and can learn social studies and some other subjects that are in the Spanish curriculum.
One school, the British Montessori School based in Alicante on the Costa Blanca, charges around £9,500 a year for daily fees and £20,000 a year for boarding.
The British School of Córdoba, which has around 450 students, charges approximately £4,300 a year for day school and £13,500 a year for boarding fees.
Fees for these schools are much cheaper than what is currently paid in the UK, where families pay on average £15,654 a year for day school and £39,000 for boarding school.
Chris Lipscomb, leader of a Devon-based global recruitment company, sends his daughter Tsarina to Kingsley School in Bideford.
But he said he and other families have started looking at private Spanish schools because of the pressure of rising fees, adding that if Labor starts taxing schoolsHe will have no choice but to send his daughter abroad.
He said: “Labour’s plan is very bad and I predict it would affect thousands of families who send their children to private schools. “They will end up looking elsewhere, especially in Spain.”
Lipscomb said the fee-paying Spanish schools he has seen are more affordable than their English rivals and he visited them recently to see what is on offer.
He added: “We have analyzed schools such as Kings College in Alicante and St George’s School in Bilbao. Last year, when we were on vacation in Oviedo, in the north of Spain, we were also given a tour of the English school in Asturias.
“In an ideal world we would keep my daughter in a British school, but several of her friends have already had to leave because it is no longer affordable. A trickle will become a torrent and many children will leave if rates rise again.”