British Museum artefacts worth up to £50,000 have been sold on eBay for as little as £40 - with items stolen from the museum appearing on the auction site a number of times over the past seven years.
And after such items began appearing online, the museum suspected that someone working there was stealing treasures from the vault before hawking them online, The Telegraph reported.
Following an investigation, a curator at the museum was identified as the worker who was dismissed after items were found to have disappeared.
Peter Higgs, who worked at the museum for 30 years, was revealed as the staff member who had been fired when items from the museum's collection were found to be missing, stolen or damaged earlier this year.
The museum announced on Wednesday it was taking legal action against an unnamed worker, who had been dismissed, and launched an independent review of security.
The staff member has not been arrested.
Peter’s son Greg Higgs identified him as the worker who had been sacked in an interview with the Telegraph, adding his dad’s name had “been completely dragged through the mud” and "sometimes where even if you’re innocent you’d just rather not have everyone speak to you all the time about it..."
The missing items include gold jewellery, gems of semi-precious stones, and glass dating from the 15th century BC to the 19th century AD, which were not recently on public display and were mainly used for research and academic work, the museum said.
British Museum chairman George Osborne said its priority was to recover the stolen items, find out if anything could have been done to stop them from going missing, and do whatever possible to prevent it from happening again.
What are the most famous collections on display at the British Museum?
The Rosetta Stone: An ancient Egyptian artefact which helped scholars decipher hieroglyphics and understand the language of the pharaohs.
The Parthenon Marbles, (formerly known as the Elgin Marbles): The marble sculptures, which once adorned the Parthenon temple in Athens, have been the subject of controversy and debate over their return.
The Sutton Hoo Treasure: The Anglo-Saxon artefacts, discovered in a burial mound in Suffolk, provide a glimpse into early English history.
The Mummy Collection: The British Museum is home to one of the world's largest collections of mummies as well as other Egyptian artefacts.
The Assyrian Lion Hunt Reliefs: These large, intricately carved stone panels depict the ancient Assyrian practice of hunting lions and are considered some of the finest examples of ancient Near Eastern art.
What items have gone missing before at the British Museum?
Items have gone missing from the museum in previous years, including several coins and medals in the 1970s and a 1993 break-in when Roman coins were taken.
In 2002, the museum reviewed security following a 2,500-year-old Greek statue being stolen by a member of the public.
The institution said at the time that the Greek Archaic Gallery had been open to the public but there was no permanent guard on duty when the 12cm-high marble head was taken.
Just two years later, Chinese gems also went missing.
In 2017, it was revealed a £750,000 Cartier ring diamond from the heritage asset collection had been reported absent in 2011.