Staff at Osmaston CofE Primary School, in Ashbourne, Derbyshire, told BBC they had not been expecting the boy to bring the World War Two weapon in for the assembly.

The bomb disposal squad was called to the institute after the grenade was discovered.

The school's head teacher Jeanette Hart said she was unsure whether the device was safe.

She said she took the explosive from the boy and placed it behind a "substantial" tree in the car park.

Army experts later established the grenade had been safe but police praised the "quick-thinking" staff, reported BBC.

'Eventful assembly'

Hart told BBC: "It was quite an eventful assembly."

"It was going fine and there was a boy who brought an old bullet case in, which I knew about, but then his friend produced a hand grenade from his pocket," she said.

"That, I was not expecting," Hart said.

Hart said she did not want to trigger panic in the school.

"It looked old and I thought it might be safe but I didn't want to take the risk," she said.

"I ended the assembly, took it off him and slowly carried it outside and put it behind a far tree in the car park. I wasn't 100% happy carrying it to be honest."

Safe

Derbyshire Police said army explosives experts later examined the grenade with an X-ray unit and determined that it was 'safe'.

A spokesman for the Matlock, Cromford, Wirksworth and Darley Dale Police Safer Neighbourhood Team told BBC: "We even got to see those [X-ray] images and [were] told a detailed analysis of how there was nothing that would set the grenade off."