A kitchen worker at an exclusive English boarding school has been arrested for trying to poison a batch of soup being prepared for students, administrators said on Wednesday.

The director of the Stowe School in Buckingham, 120 kilometres north-west of London, said a household cleaning agent was put into the carrot and coriander soup, but no one was harmed because the soup wasn't served to students.

Kitchen staff became suspicious of the soup because of an acrid smell, head teacher Anthony Wallersteiner said.

"Before any meal is taken up from the kitchens to be served the food is tested, and it was during the routine sampling that one of the duty chefs discovered there was something acrid in the soup that was being prepared," he said.

The soup would have been offered to about 650 students who usually have dinner at the school, officials said.