Hi i have first hand experience with this one !
my mum and dad were at a wedding there years and years ago subsequently photos were developed (no digital back then) and low and behold devil picture !
but there is a very easy explaination , it was taken in the main hall upstairs the bar had the shutters down and the reflection off the shutter from the flash at the far right hand side cast a butterfly wing effect reflection in the corner of the bar ! simples , my dad however did not want to keep the photo in the house because of the hype at the time in the papers etc ! im sure the negitive is knocking about somewhere