A judge in England has called the wrong horse the winner in a hurdle at Sandown based on a photo from the first of two winning posts on the track.

One For Rosie, trained by Nigel Twiston--Davies, was announced as beating the Hughie Morrison-trained Third Wind.

But it transpired the call had been based on a photo-finish print from the first winning post on the track, when in fact the second one should have been used for the two-and-a-half-mile (4000m) hurdle by which time Third Wind had edged in front.

After a lengthy delay, the result was reversed.

"It's very depressing, but mistakes happen. We did get beat, we've seen it there (replay)," Twiston-Davies said.

"It's a great shame, but we've still got a lovely horse.

A number of bookmakers opted to pay out on both results.

"Given the confusion, we have made a decision to pay out on both, but it's an infuriating thing to happen at any time." Coral's David Stevens said.

The British Horseracing Authority said it would conduct a thorough investigation.

"The photo-finish image that was sent to the judge, and then subsequently to the stewards, by the racecourse photo-finish operator was from a camera which had been left focused on the winning line for the chase course," the BHA said in a statement.

"There are two cameras in operation, a primary and a secondary, which were tested by the operator as part of routine pre-race checks on both winning lines prior to racing. The primary camera was then not correctly re-aligned to focus on the winning line for the hurdles course.

"We will be investigating this incident thoroughly as a matter of priority to understand all of the circumstances involved, this will include engagement with the external racecourse contractors who operate the photo-finish system."

The mistake was discovered before jockeys weighed in but several bookmakers had paid out and had to then pay out again on the correct winner.