An artist who helped mastermind a Willy Wonka-style treasure hunt for four bank notes, worth an estimated £50,000, admits the only still-hidden fiver could be anywhere in the world.

Micro-engraver Graham Short etched Jane Austen's face into the transparent part of the new plastic Bank of England £5 notes.

But true to Roald Dahl's classic tale of Charlie and the Chocolate Factory, while three were quickly discovered, no one has yet publicly laid claim to the fourth.

Mr Short's friend and fellow artist, Tony Huggins-Haig, who launched the project, said around 5,000 people have called up falsely claiming to have found it.