A fire official has confirmed contractors caused a chemical reaction which led to the mass evacuation of a Twickenham school today.

Fourteen fire engines and nearly 20 ambulances were called to St Catherine's School in Cross Deep at about 10.52am following reports of chemical leak.

It later emerged the incident was caused by contractors who were working in the swimming pool area of the school.

It is thought they poured two chemicals down the drain resulting in a chemical reaction.

Eight children and four adults were taken to hospital as a precaution.

Simon Brownings, Kingston station manager, said a number of the victims had complained of runny eyes believed to be caused by coming into contact with fumes.

He said: "We were called to a suspected chemical leak at the school.

"Crews very quickly ascertained what it was and what had happened.

"There are contractors working at the school and unfortunately they mixed the chemicals together and caused a reaction in one of the drains."

More than 150 children were at the school attending the Barracudas Summer Activity Camp.

They were evacuated and taken to St James' Independent School for Boys opposite for safety.

They returned to St Catherine’s just after noon when the all-clear was given by the fire brigade.

Headteacher, Sister Paula Thomas, confirmed the incident happened at the school’s swimming pool.

She said the emergency services were called after people in the changing area of the pool smelled fumes.

She added: “It was very unnerving seeing everyone arriving.

“They were not wet chemicals so no one was burnt.

“The paramedics said they [the children] were all fine but would take some of them to hospital to check them out.”

Staff and drinkers at the nearby Alexander pub were told to stay inside by police while investigations into the reaction were carried out.

Manager Erica Wiles said: "The emergency services sort of all descended.

"I'm just amazed it was to do with chemicals.

"It was all a bit chaotic but the kids seemed to be ok.

"It's not good for trade though."

Pope’s Grove was cordoned off by police while fire crews dealt with the incident.

It has now been reopened.

A London Fire Brigade spokeswoman confirmed Thames Water had also been called.

Are you watching the drama unfold? Call the newsroom on 020 8744 4272 or email jkilvington@london.newsquest.co.uk.