A nursery school has been closed following the discovery of carbon monoxide during a routine boiler check.

Children were told to stay away after traces of the potentially deadly gas were found by maintenance staff.

Education leaders today insisted children had not been put at risk, although they did not know how long the boiler had been faulty.

No children have been reported as having symptoms associated with exposure to the gas, which is odourless and colourless.

The nursery at Whitehawk Primary School in Whitehawk Road, Brighton, has been shut for the past three days following the discovery on Friday evening.

Electric heaters have been installed and it was due to open again this morning after a final round of tests.

The 80-pupil nursery is based in a separate building from the main school, where the 420 pupils have not been affected.

A spokesman for Brighton and Hove City Council said the leak was detected in the boiler room, which is directly below the staff room.

He said: "There were small amounts of carbon monoxide leaking from the boiler serving the building in which the nursery is housed.

"As a result the nursery was closed during Monday while engineers came to fix it.

"The engineers came back on Tuesday to check their work and found they were still able to detect some carbon monoxide in the boiler room.

"Safety is always our first and only priority in these situations so a decision was taken to close the nursery again.

"The boiler will remain off until we're absolutely sure the problem has been fixed.

"In the meantime, we're putting in electric heaters to enable the nursery to open as usual and would like to reassure parents there is no risk to children's health."

One father said he was angry parents had not been informed earlier of the reason for the closure.

Michael Hill has taken his four-year-old daughter to the doctor, fearing she was showing signs of carbon monoxide poisoning.

Mr Hill, 36, a caterer, said: "My daughter has been coming home from school and just sleeping two or three hours. She is always feeling sick and complaining of a bad stomach. I can't believe the school didn't have a detector in place."

There is no statutory requirement to fit carbon monoxide alarms in schools, although Government guidelines say appliances should be checked every 12 months.

The council spokesman said: "Neither the school nor the LEA have had any reports from doctors about children or staff suffering any symptoms that could relate to carbon monoxide."

Councillor Pat Hawkes, head of children, families and schools at the city council said: "This is very unfortunate but we have the highest standards of health and safety in all our schools.

"There are the most stringent ground rules about when a school can open again."

Headteacher Garry Pendergast was at a parents' evening yesterday and was not available for comment.

Carbon monoxide is produced when heaters fail to burn properly.

Breathing in the gas replaces oxygen in the blood and can cause headaches, dizziness, nausea and convulsions.