A catering assistant at a prestigious private school has been arrested after allegedly trying to poison a batch of soup intended for pupils and teachers.

The soup was ready to be served up for an evening meal at Stowe school, in Buckinghamshire, when a member of staff noticed a suspicious smell.

Service was aborted and police were called to the £6,000-plus a term school, which counts Richard Branson among its alumni, before officers arrested a 58-year-old man at his home near Brackley, Northamptonshire, on suspicion of administering poison with intent to endanger life or inflict grievous bodily harm.

Police said today there was no apparent grudge or grievance that would suggest a motive for tampering with the carrot and coriander soup.

At a press conference today at the school, headteacher Dr Anthony Wallersteiner said it is believed the product used was a "household cleaning product that would be used in any domestic kitchen".

He added: "From the discussions I have had with the line managers of the catering department we do not know of any grievances or previous issues with this individual."

Chief Inspector Henry Parsons, from Thames Valley police, said: "The police and the school are not aware of any issues at all, any motive of this at this early stage."

Wallersteiner said: "This was a batch of soup that was being prepared for the evening meal and that was quite an ordinary batch of soup, there was nothing untoward about it.

"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."

Dr Wallersteiner said the employee, who had worked for the school since January 2007, had since been suspended under the school's disciplinary procedure pending a full inquiry.

He has been instructed that under no circumstances may he enter the school premises, the school said.

He said: "I would like to reassure parents that no pupil or member of staff was affected in the incident and, given the rigour of the procedures, neither the pupils nor staff were put at any risk."

He said the member of staff who tested the soup had tested a very small quantity and said "it was immediately spat out because it tasted so foul".

"I have been in contact with the medical centre and I have asked whether they have spotted any unusual entries regarding food poisoning or food-related illnesses and they have said that as far as they are aware there has been no unusual activity in the medical centre.

"We have had a couple of viruses and normal seasonal flus but nothing gastric or food-related. There's nothing to suggest it was anything other than a one-off."

Thames Valley police said the suspect was not interviewed after being arrested on 12 March as he was "unfit to detain for health reasons". He has been bailed until 29 March.

The catering section of Stowe school's website says food is provided by a "very experienced, in-house" team.

"The menus are varied, nutritionally balanced and provide a wide choice at each meal to suit all tastes, using fresh ingredients wherever possible," the website says.