Howzat for a mystery: Did Garry Sobers hit it for six sixes - or is £26,000 ball an imposter?

It's the stuff of boyhood dreams. Teenager Richard Lewis gazed across the cricket pitch at Swansea's St Helen's ground as the great West Indian Garry Sobers hit six consecutive sixes in one over - for the first time in the history of the game.

The ball in the last of Sobers's sixes disappeared out of the ground in the summer of 1968, and the 17-year-old ran off to retrieve it. That small, battered sphere was sold at auction by Christie's last month for £26,400. But doubts have now been cast on the ball's authenticity.

Mr Lewis had presented it to Sobers at the Glamorgan ground the following day, and it was supposedly taken back to the player's Nottinghamshire team HQ to be stored in the Trent Bridge museum.

Roger Davis, the player who caught one of the sixes but fell over the boundary in the process, said he had been told that the ball was stolen from the museum. But it turned out that it was never put on display.

Peter Wynne-Thomas, the curator at Trent Bridge, has investigated the saga of the mystery ball. "There was a long, long, long rumour ever since I started here that the ball was in the museum," he said. "Sobers brought it back but it was given to a Mr W H Gough, the chairman of the supporters' club, and it was put in the Eddie Marshall Bar."

From there it passed into the hands of the supporters' club secretary, Josie Miller. She passed it on to Christie's after keeping it in her make-up drawer for almost 40 years.

The doubt has arisen now because of the ball's manufacturer. It was made by Dukes, a major supplier, but Glamorgan officials and former players insist that the Welsh county only used balls made by Stuart Surridge at that time whenever they played at Swansea because they were supplied by Bill Edwards's sports shop next to the ground.

Peter Walker, the broadcaster who was playing for Glamorgan that day, says: "I think this ball is a phoney ... What I think is sinister is that Christie's should have heard from three eyewitnesses who were on the field and from Bill [Edwards] that it was not a Dukes ball that was used. They should have taken a deep breath before saying that theirs was definitely the one."

Walker spoke to Malcolm Nash, the unfortunate bowler at the time and now the US junior cricket coach in Kansas. He said: "I have absolutely no doubt that only one ball was used that over and that it was a Surridge. I should know, because I was the one who had to let it go each time and then watch it disappear."

That brings up the question of how many balls were used during the five minutes of mayhem. Mr Edwards, 85 but still running his shop, says: "Take it from me, it isn't so that only one ball was used."

Sobers told Walker: "I've no idea. Down the years I've lost count of the number of people who've come up to me saying they'd gone to an auction and bought a bat I was using." The bat with which he hit the six sixes was sold at a Melbourne auction for £54,257 six years ago.