Armed officers detained the teenager an hour after the stabbing in Stoke Orchard, about five miles south of Tewkesbury, on Monday morning and recovered a knife.

The arrested boy is from Tewkesbury. Police have not given his name and he remains in custody.

A motivation for the attack remains unclear but it is not thought to be terror-related, police said.

The teacher, named locally as Jamie Sansom, was in a stable condition in hospital after being stabbed. Police confirmed on Monday evening he had been discharged.

Police were called just after 9am on Monday over a "threat to a teacher", Assistant Chief Constable Richard Ocone told reporters.

"Minutes later we received a call from the ambulance service telling us that a male teacher had been stabbed in a corridor at the school," he said.

No one else was injured.

Tewkesbury School, in Ashchurch Road, was put into lockdown following the incident and carefully searched to ensure there was no further danger.

Two other schools in the area were advised to close their doors.

The National Police Air Service were deployed to track the suspect down.

Initially, it was thought the suspect had "hidden himself within the school grounds", Mr Ocone said.

"Our officers, including specialist armed police, attended and carried out a thorough search. This search was both complex and meticulous in nature as we sought to ensure there were no further injured parties as well as seeking the arrest of the suspect."

Police will remain in the area in the coming days as the investigation continues, Mr Ocone said.

A crowd of about 100 people gathered outside the school after the stabbing and uniformed officers stood on duty at its entrances.

Sky News correspondent Dan Whitehead spoke to Sarah Penny whose daughter Issy was inside at the time.

"Mum, I'm really scared," the 13-year-old messaged.

"They had guns, they had armed police."

A spokesman for Tewkesbury School said "no decision has yet been made on when the school will reopen".

He added: "We will be drawing up plans to support our students and staff in the wake of this incident."

The school, a state secondary, "requires improvement", according to an Ofsted report published in January.

Prime Minister Rishi Sunak's thoughts are with those affected, Downing Street said.

Education Secretary Gillian Keegan said she was "deeply concerned", adding: "We are closely monitoring the situation and remain hugely grateful to the emergency services.

"My department is on hand to support the school."