Police in riot gear were sent to raid a central London gallery after it put a fake bomb in the window.
Alison Southward, manager of Mauger Modern Art, in Rochester Row, Westminster, said she arrived at work to find officers in riot gear outside.
A police spokesman said it had received reports of a "suspicious" device.
The gallery said the "comedy bomb" was strapped to a step ladder and featured "Western-style bunches of dynamite" and an alarm.
Ms Southward said: "I arrived to open up the gallery, and a riot van and two squad carriers were outside.
'Sent to prison'
"The officers told me they were just about to break the door down.
"They told me having something that looks like a bomb is a criminal offence and I could be sent to prison."
Once she explained that the bomb was not real they relented, however.
She said: "When I explained it was an installation, they said that as long as we put up something in the window to say it's a piece of art, we'd be able to keep it."
Gallery owner Richard Mauger described the installation by artist Paul McGowan was "a comic illustration".
He said: "It's obviously a comedy bomb. It's laughable."
A Metropolitan Police spokesman said police were sent to the gallery at about 1020 BST.
He added: "Officers attended and ascertained that the item was an art installation."
Mr McGowan's artwork has appeared at the Eden Project, in Cornwall since 2008.
He said of his work: "The physical and emotional landscape is changing and there is so much tension and anxiety all around us."