Daniel Radcliffe and Helena Bonham Carter on the Pembrokeshire Coast set of 'Harry Potter and The Deathly Hallows'. (WENN.COM file photo)

A top secret script for the final Harry Potter movie was found abandoned in an English pub after the film's crew left it behind on a boozy night out.

A reveller discovered the screenplay for Harry Potter and the Deathly Hallows in a bar in Hertfordshire, England - near to the studio where the final instalment of the wizard franchise is filmed.

The script, which features dramatic changes to the book's narrative and was stamped as 'Private and Confidential', was handed to reporters at Britain's The Sun newspaper - who then returned it to movie bosses at Warner Bros. studios.

According to the publication, studio executives have launched an immediate investigation into how the top secret script was casually left behind in a public place.

A source tells the newspaper the crew was celebrating in the pub after catching up with delayed filming.

The insider says, "They'd got behind schedule in filming but then caught up, so they went out for a celebratory drink which led to many more.

"There was a huge group. They were here all night, laughing and joking, chucking back beers. They usually come down for a session on a Friday, but because it was Easter they were in a day early.

"Daniel Radcliffe is the only member of the cast who has been known to come down and have a laugh with them, but he wasn't there that night."

The man who found the script adds, "I couldn't believe my eyes. I know guys that work on the film drink in the pub, but it's very embarrassing that someone could just leave it there. I'm glad I've helped to stop any surprises being leaked."

A rep for Warner Bros. says, "We are grateful to The Sun for the safe return of this script."