A large wall mural by "guerrilla artist" Banksy has been mistakenly painted over by a council's graffiti-removal contractors.
A graffiti removal team painted over the mural
The valuable 25ft-long artwork, on the side of garages in Bristol, was covered with a coat of thick black paint.
Bristol City Council said it wanted an investigation into the blunder. The council has ordered all Banksy works in the city to be preserved.
Someone has now sprayed the words "Wot no Banksy?" over the obscured work.
The mural, one of Banksy's early pieces, had featured a collection of blue shapes with the artist's trademark tag.
Other tags by Banksy have been left on a railway bridge further along the road at the site in Albion Road, Easton.
Gary Hopkins, of Bristol City Council, said the contractors, Nordic, had been asked to tackle graffiti adjacent to the Banksy work, but wrongly targeted the piece itself.
"The Neighbourhood Renewal Team was told to remove graffiti next door to the piece by Banksy," he said.
"We would have to take action against the contractor because the city council has not given instruction for the removal of any Banksy work - we are aware that it's actually quite valuable so we have specific instructions not to remove any murals by Banksy," he said.
Contractor Nordic was not available for comment. Banksy also declined to comment.
Some of Banksy's pieces have fetched a high price among modern art collectors.
In February a picture of pensioners bowling with bombs sold for £102,000, breaking a record for his work.
But the Lazarides gallery in London, which sells his works, said it would have been wrong to place a value on the former Bristol mural as it might have tempted someone to remove it.
In November 2006, a gang of thieves dressed as council workmen attempted to steal a Banksy piece painted on the door of a derelict building in Liverpool.