An Antiques Roadshow guest was told a piece of art, that should have been worth £20k, was actually worthless.
Expert Rupert Maas was tasked with valuing a signed Banksy piece on tonight's show.
Mr Maas quickly identified that the painting has been torn off a building as it sat on an old steel plate.
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The guest explained during his time living in Brighton, he saw the 'loose' piece on the lido on the seafront and pulled it off.
The piece appeared to be from around 2004, and the guest had brought it to Antiques Roadshow to have it valued.
However, Mr Maas explained there was a problem with the piece the guest had brought in.
He said: "Now, that's a tricky thing because the thing about Banksy, and he's not the first to have done this, of course, is that he manages his brand very, very carefully indeed.
"He has a website where you can go in and apply for a certificate of authenticity of his work.
"And then he or his team will issue one if they think, first of all it's authentic and if they think that it has not been removed from the public domain for which it was painted and into the private."
Mr Maas continued: "Now, that might be a reason for not issuing a certificate of authenticity.
"He calls it pest control which is rather good considering the rat features rather a lot in his work."
The guest explained that he had tried to get a certificate of authenticity, however, the team came back and said they couldn't claim it was an original Banksy.
Mr Maas said: "I think the message here is that if you do see a piece of graffiti art out there, leave it, leave it for the public.
"I'm not lecturing you, I'm just saying that without that certificate it's just very difficult to sell.
"With it, it might be worth £20,000. Without it, you're nowhere.
"I'm sorry."
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