Tweeddale Primary School faced a crisis last week, after one of its year 6 students allegedly brought a knife on to school grounds.

Sutton police were called to the Carshalton school after parents noticed an 11-year-old student brandishing a knife in the playground before class.

He has since been excluded from the school.

A source close to the school, who did not want to be named, said they believed the boy had brought the knife to the school after an alteraction with two other students the day before.

"He was angry at another child and his brother, who had called his mum some names," the source said.

"And when he came to school that morning, he was holding this big three-inch kitchen knife in his hand near the playground.

"He wanted to make all the children know he had a knife."

"But the knife was disposed of as soon as the boy realised other children's parents had spotted it."

"He threw it on to the play centre roof and then the caretaker had to go and collect it."

"Next thing I knew, there were police everywhere and the boy's mum was called in, too."

The mood around the school remained one of shock, said the witness.

"Never in all my years would I expect a child to bring a knife into a primary school, because they are aware of the serious damage it can cause," they said.

Sutton police have confirmed an 11-year-old boy was arrested at school last week.

He has since been released on bail, pending further inquiries.

The anonymous source said they hoped the boy had the book thrown at him.

"He got as far as the playground where he could have used the knife, so the police need to make an example of him," they said, also taking aim at the school's administration for "trying to cover up the incident".

"If it was my kids at the school, I'd want to know what happened so I could find them another school," they said.

"But it's all been hushed up."

They said the school had held a special assembly for the year 6 group, informing them about the dangers of knives.

"All the year 6 parents were sent a letter informing them of the incident, but I don't think the rest of the parents know," they said.

But a spokeswoman for Tweeddale School said the school was working with the police to ensure all pupils, parents and guardians were reassured following what they labelled as a "one-off event".

"The safety of pupils is our number one concern, which is why we contacted the police as soon as we became aware of the incident," they said.

"This kind of behaviour is unacceptable and the child has been excluded."

Sutton police spokesman Colin Walden said: "We are taking a robust and pro-active stance to tackle the carrying of knives in the borough."