Several parents paid two years in advance to secure a 10 per cent discount but are now faced with finding new schools and paying all over again. A number are planning civil actions against the school and have called for an investigation into its finances.
They are particularly angry with Robert Chenhalls Walker, former chairman of the board. Parents say there was always a lack of transparency in the board's dealings. Jarek Garlinsky, the new head, believes problems could have been avoided if a closer watch had been kept on spending. "The seeds were sown well before the deficit of this year came to light," he said.
Although the school is a member of the European Council for International Schools (now the Council for International Schools) and advertises itself as such, it is not "accredited".
Jerry Percy, CIS accreditation officer, said: "Going to an accredited school is a reasonable safeguard for parents."
Accreditation involves a strict process of inspection and reporting, including on financial matters over several years. CIS teams are sent into accredited schools at regular intervals to observe teaching practice and to look at the books.
Mr Percy said failure to report deficits would be a breach of CIS standards. He said although this may not have prevented the problems it would have brought them to light earlier so that a solution could be found.
However, he admitted there could be confusion for parents between "membership" of CIS and the more rigorous "accreditation".
Members merely have access to CIS services, which include teacher recruitment websites. "Perhaps the distinction is not as clear as it should be," he said.
However, the school is accredited by the French government, to provide school-leaving qualifications, and by the International Baccalaureate Organisation in Geneva. But neither offers financial safeguards.
With international schools burgeoning as a business sector, countries such as Thailand and China are setting up accreditation schemes for operators.
These include rules on financial transparency.