The "guerrilla artist" Banksy is believed to be behind a piece of street art depicting three shadowy figures eavesdropping - three miles from the Government listening post GCHQ.
The artwork, which appeared in Cheltenham on Sunday, depicts three men wearing sunglasses and using listening devices to "snoop" on a telephone box.
The piece has already attracted hundreds of visitors.
Banksy has not yet claimed the work but it bears his hallmarks, say experts.
Vince John from the 1loveart gallery in Bristol, which sells urban and street art, said he was "70% to 80%" sure it was by the famous artist: "From what I can see it certainly looks like a Banksy.
"It's certainly in his style and has the supporting cast of characters that you'd expect from one of his pieces.
"It's taking a swipe at GCHQ and commenting on the establishment which is something that he does very well."
Cheltenham street artist Dice67 claimed he had been told the artwork, which appeared on the corner of Fairview Road and Hewlett Road on Sunday morning, is indeed by Bristol artist Banksy.
"It's been all over the art forums. He's tipped off a couple of people to come and see it - one guy flew in from France yesterday to take some photos of it.
"I've heard rumours he's been living just down the road from it for the last week checking everything out and preparing the ground.
"I'm pretty sure it is [a Banksy]."
A GCHQ spokesperson said: "This is the first time we have ever been asked to comment on art.
"Although we are not qualified critics, we are as intrigued as the rest of the residents of Cheltenham about the appearance of the mysterious artwork.
"For those who are interested, our website gives a glimpse of what modern-day intelligence operatives are really like, although some may be disappointed by the lack of trench coats and dark glasses."
Banksy's last known works of art were created in New York last October during a month-long residency.