People who carry knives are being urged to ditch them at police stations as part of a nationwide amnesty which starts today.

The amnesty comes just days after a Year Seven pupil was excluded for one day from Matthew Arnold School, Oxford, for carrying a blunt-edged knife he had taken from an art room.

He was reported to staff after he verbally threatened a fellow student in an argument over a girl on Thursday afternoon.

The school said that the incident was in a different league to the fatal stabbing last Thursday of 15-year-old Kiyan Prince outside the gates of his north London school.

Matthew Arnold School headteacher Katherine Ryan said: "It was a battered old round-edged dinner knife that was covered in paint. It was used in the art room for scraping paint out of pots. It was not sharp.

"This was nothing like the dreadful incident involving the poor child murdered in London my heart goes out to his family.

"It was an incident of bullying. He did not use the knife to threaten anyone, but the kids had seen him with it and put two and two together.

"We don't tolerate bullying in any way and we do take incidents seriously, whatever level they are.

"We want children to be safe and happy at school and we will do whatever it takes to achieve that. The little boy concerned knows he has done something wrong and he has apologised. I'm just pleased that the children do come straight to us and tell us when they are worried."

The knife amnesty, announced by the Home Office earlier this year, aims to reduce the number of knives in circulation.

There were 293 crimes involving knives in Oxfordshire last year, with one person murdered and 66 injured.

Roger Mayne, crime reduction manager for Oxfordshire, said: "We are reaching out to parents, families, friends and school teachers to support us in persuading people who carry weapons to give them up. The consequences of not doing so could be devastating."

John Mitchell, the council's spokesman for children, young people and families, said there was no evidence to suggest there had been a significant increase in incidents involving knives or weapons in Oxfordshire schools.

He said: "Schools take such incidents very seriously and this is reflected in their behaviour policies and their responses to incidents when they do occur."