A private school in Esher has been forced to apologise to parents after teachers discovered they had been using an out of date iGCSE chemistry syllabus.

The blunder came after 25 Year 11 Claremont Fan Court School students sat the first of three iGCSE chemistry papers, but found they had not been taught the topics in one of the questions.

Headmaster Jonathan Insall Reid apologised “deeply” for the error in a letter to parents, seen by the Surrey Comet. Tuition at the school costs £5,345 a term.

He said: “The senior school’s investigation of circumstances of this error and the effects it will have on Tuesday’s examination will be thorough and is underway.

“Included in this investigation will be contact with the exam board. The results of this investigation will be forwarded to you as soon as possible.

“The head of science faculty, head of chemistry and the chemistry department join me in apologising for this error made by the school and I give you my assurance again that we will do all that we can to ameliorate this situation.

“The head of Year 11 and staff at this school will work very hard in the coming weeks to maintain confidence in each and every one of our Year 11 pupils that has been building up over many years.”

In the letter, Mr Insall-Reid listed several revision sessions for the coming week that would cover the missed topics.

An iGCSE is an international two-year qualification programme that leads to externally set, marked and certified examinations from the University of Cambridge.

The school, which is set in the historic grounds of the Claremont Estate, said in a statement on Wednesday to the Comet: “The changes in the 2016 iGCSE chemistry syllabus are small. The iGCSE chemistry pupils were disadvantaged to approximately 4 per cent of the full exam score.

“The school immediately organised a series of chemistry classes, tutorials and clinics to cover the updated material.

“These sessions have taken place each day and chemistry staff were available throughout on a one-to-one basis to support iGCSE chemistry pupils in preparation for the second and third iGCSE chemistry papers this coming Thursday.

“We are confident that all material has now been covered. We deeply regret this error and have apologised to iGCSE chemistry pupils and parents. A full investigation is underway to identify how this situation occurred.”

Esher councillor David Archer said: “I think the error needs to be put right as fast as humanly possible.”