A limited edition print of Monkey Queen (2003) by Banksy next to Grin Reaper and Gangsta Rat (Red) at the Hofa Gallery in Mayfair, London, in 2020

Theguardian_ His identity has long been a matter of speculation and investigation, but Banksy may be forced to reveal his real name if a dispute over a print of the late Queen Elizabeth depicted as a bejewelled primate ends up in court.

Two art collectors are taking legal action against the graffiti artist’s company, Pest Control, following its apparent refusal to confirm the authenticity of Monkey Queen. After three years of trying to get an answer, Nicky Katz and Ray Howse have lost patience and are suing Pest Control for breach of contract.

They point to Pest Control’s website, which states that it will issue a certificate of authenticity for “paintings, prints, sculptures and other attempts at creativity”. It likens the certificate to “an MOT for the art world”: “[It] means you can buy, sell or insure a piece of art knowing it’s legitimate and the wheels won’t fall off.”

Banksy, known for his stencil-based images, has described himself as a “quality vandal” ridiculing authority figures through artworks in public places. His partially shredded painting Love is in the Bin sold for more than £18.5m at auction in 2021, while his signed prints sell for five and six figures. Pest Control was set up by the artist in 2008 after fake prints were sold online and it plays a key role in the market for his work. An authentication certificate is vital to achieve the maximum price when selling his work, it has been claimed.

Banksy’s real identity has been a celebrated mystery among the media and public for decades. Massive Attack’s Robert Del Naja, Jamie Hewlett of Gorillaz and Neil Buchanan, the former host of TV’s Art Attack, have all been suspected.

In 2008, the Daily Mail “unmasked” him as Robin Gunningham, a then 34-year old former public schoolboy, although the artist denied this. No one has been able to absolutely link Gunningham and Banksy. To do so would destroy his mystique and potentially the price his work fetches.

A 2003 interview with a BBC reporter contains the only known instance of him revealing his first name. In the recording, which has recently emerged, Banksy is asked if his real name is “Robert Banks”, to which he replies: “It’s Robbie.”

Katz and Howse say they have tried in vain to obtain a verdict from Pest Control either way on whether Monkey Queen is one of Banksy’s genuine prints from a limited edition of 150.

They sent the artwork to Pest Control, explaining that they had acquired it for £30,000 in 2020 from the estate of a recently deceased, established Banksy collector, but that there seemed to be noaccompanying paperwork detailing its collecting history.

Katz, 65, a Londoner who owns a quarry and an art collection that includes a large number of Banksy works, said that Monkey Queen is worth between £55,000 and £70,000 and he is outraged by Pest Control’s delay: “We’re in no man’s land, and it’s a lot of money. They claim to be the official validators of this artist’s work. But this has been going on for three years. They’re just sitting on the fence – they won’t say whether it’s right or wrong. We have had our tails pulled for the whole three years.”

He said, addressing Pest Control: “‘You’ve had the work; you’ve inspected it. Is it right or is it wrong? That’s the service that you claim to provide. If it’s wrong, that’s OK, because we will have a claim on the estate the piece was bought from. If it’s right, great. Just give us the paperwork we need to validate it.’ They’re not providing a proper service.”

Legal action is now the only option, he added: “We’re suing Pest Control for breach of contract. They’ve had three years to do what I paid them [£50] to do, which by any standard is plenty of time to deal with the situation.”

The Banksy artwork Well Hung Lover, in Bristol, was defaced by paintball in 2009

He added: “I am very disappointed with Banksy. He has made it impossible for anyone to validate a piece of his work without his certificate. That affects the value of his work dramatically. If I had a painting by Leonardo da Vinci, there is no ‘Leonardo Control’ to validate it. I would simply take it to the experts to tell me whether or not it’s a work of art by Leonardo da Vinci. In the case of Banksy, even if you have expert opinion saying that the piece is one of his, if it doesn’t have a Pest Control certificate, you can’t rely on that expert.”

John Brandler, a leading specialist dealer in graffiti artists, said: “I believe that this is a genuine Banksy, but it has taken three years for these ­collectors to get nowhere with Pest Control. This is pure market manipulation, because Banksy will only certify works that he wants particular individuals to have.

“That’s not authentication. If someone discovers a Titian in an attic, nobody says: ‘Who are you and why have you got it?’ It’s a Titian or it isn’t. With Banksy, it’s: ‘Who are you and why should I tell you?’”

But Brandler observed that Banksy’s prices are “well down on what they were three years ago”. He singled out Police Car, which depicts a vehicle lifted up on bricks: “Two to three years ago, it would have fetched between £1.5m and £2m. It sold in Paris about a month ago for €300,000.”

Pest Control said: “Our authentication process is robust and thorough and sometimes protracted. We have issued many thousands of certificates of authenticity.”