The cast-iron bell, still attached to its wooden headstock, was handed back to staff at Ashville College, Green Lane, Harrogate, by farmer Russell Oliver, 68.

Mr Oliver, of Butsfield, near Birtley, County Durham, and another ex-pupil took the bell, hanging outside the school's Elmfield boarding house – now the science block, in 1957.

Afraid of possible consequences if he returned it, he kept hold of it. That was until his wife, sick of seeing it gathering dust in their garden shed, put it in the back of their Range Rover before heading to this year's Great Yorkshire Show. In Harrogate she revealed what was in the boot and made him take the bell back before heading home last Friday.

Mr Oliver said: "It was a prank carried out at our first old boys' reunion. After a few drinks at a local pub we came up with the idea of taking the bell down and leaving it outside the door to the head's study.

"We drove back to the school in the early hours and, as quietly as possible, began unscrewing the coach bolts that secured the bell to the tree where it hung.

"Once free, the clapper struck the bell and lights in the boarding house started coming on. We panicked, threw it into the boot of my TR2 and drove to my friend's house in the town centre."

But the car's exhaust was loose and the noise of it scraping on the road – together with the bell ringing – woke a neighbour, who called the police. An officer was at the door in minutes.

"We were scared to death and didn't dare answer the knocking. After that we were afraid to take the bell back. I'm glad I have now finally got around to handing it back, even if it is more than half a century later than originally planned."

Ashville College headmaster Andrew Fleck said: "This is a remarkable story and naturally we are delighted when any school property is returned, even if 51 years have passed.

"We will now look at cleaning the bell and displaying it in a suitable place – one where it can't be removed by pupils wishing to emulate Russell's stunt.

"We are grateful to Russell for handing it back and he can be safe in the knowledge that there won't be any repercussions."