Artworks by Damien Hirst have reportedly plummeted in value since he shattered the world record for an auction sale in 2008.

The Beautiful Inside My Head auction raised a whopping £111m for the artist over two days, even as the financial markets collapsed amid the subprime mortgage scandal.

Artworks are often bought by collectors as long-term investments, with the hope that they will increase in value over time as the artist's reputation grows.

However, experts at website Artnet have discovered that 17 of the 19 Hirst works sold since the 2008 auction have actually depreciated in value, with a total loss of around £2.2m.

A painting of a skull titled Beautiful Mider sold for £670,000 in 2008, but was sold last year for £449,000. The Times notes that the loss for the seller will have been worse due to buyer's premium, seller's fees and storage costs.

Tim Schneider of Artnet said it was not a case of one or two works dragging down the average worth. "Instead of a formaldehyde tank, the best fluid measure here is a bloodbath," he wrote. "Is this grim total just a matter of a few horrendous results pulling down the rest of the group by association? Individual results thunder back a loud 'no'."

Art economist and author Don Thompson said it was unlikely that collectors who bought Hirst's work as an investment would ever recoup the money they spent. "The value of his traditional work, taxidermy animals, spot paintings, spin paintings, probably peaked with the auction," he said.

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Art specialist Philip Hook warned collectors back in 2013 that the "bubble" maintained by Hirst's PR machine would eventually burst.

Speaking at the Cheltenham Literature Festival he said: "An artist who is simply very good at playing the market and is good at marketing himself, he is the most in danger of [his art] suffering when he dies," he said.