Twenty-six children were taken to hospital today after a gas canister was set off in a school.

Part of 1,100-pupil Priory School in Lewes was sealed off as a fleet of ambulances took the contaminated children to hospital.

None was seriously hurt but three suffered breathing difficulties.

The 26 children, aged 11 to 12, were checked by accident and emergency staff at the Royal Sussex County Hospital, Brighton, before being allowed home.

Head teacher Martyn Ofield said: "This morning a Year 7 student let off a spray canister in the boys' changing room. We are not certain what was in the canister.

"The changing room was evacuated very promptly, the ambulance service called and 30 Year 7 boys in the changing room were taken to the Royal Sussex hospital for precautionary checks.

"The school has telephoned and informed parents of those children involved."

A spokeswoman for the Sussex Ambulance Service said: "The boys had all been taken out into the fresh air outside the school. Some were very upset."

The school was not evacuated but the area round the changing room was sealed off as firefighters in chemical suits began decontaminating the changing room.

Police were called to the school in Mountfield Road, Lewes, at 10.15am.

A force spokeswoman said: "We received a call that what is believed to be a CS spray canister was set off in a boys' changing room.

"We would remind the public that these sprays are not only dangerous but it is an offence to be in possession of them in this country."

An 11-year-old boy was being questioned by police this afternoon.

CS is a tear gas which rapidly causes a severe burning sensation in the eyes, nose and throat, a slowing of the heart rate, rising blood pressure and coughing. In some cases it causes nausea and vomiting.