A Bristol piece by street artist Banksy has been vandalised in an apparent attack by a rival artist.

The

stencil, which appeared near Bristol city centre four years ago and featured a boy creeping up behind a

sniper with a paper bag in his hands, has been covered in black paint

and graffiti scrawl.

The vandalism has been signed "Team Robbo".

apparently a reference to King Robbo, regarded as a founding father of

the London graffiti scene.

The pair, or perhaps their followers, have been blamed for defacing or manipulating the other's work over the past two years in London but this is the first known Bristol defacing due to the feud.

Staff

at Wallace & Gromit's Grand Appeal, which supports Bristol

Children's Hospital, say they had come to think of it affectionately as

"our Banksy" since its appearance four years ago.

They believe the

work, which appeared after they appealed to Banksy for help in

deterring people from daubing graffiti on their building, may have been

a gift from the notoriously secretive street artist in response to

their plea and they hope he will help them again.

The

charity told the Evening Post the Banksy work has brought fans of the

street artist into its offices to make donations and buy merchandise

and fears the damage to the artwork could affect income. 

Director Nicola Masters said she was aghast when she saw

what had happened to the work over the weekend.

"A

few years ago we were getting lots of graffiti all over the front of

the building. It wasn't pleasant for families trying to come into our

offices to hand in their donations.

"It happened all the

time and one of my colleagues sent a note to Banksy through his website

saying that we were fed up with it and did not know what to do.

"What I like to describe as our Banksy, although we know we cannot claim it to be ours, appeared after we posted the note.

"We

have always thought of it very fondly and always felt very proud of it.

We always thought he did it for us, and essentially for Bristol."

The council cleaned up a previous Banksy mural – of a naked man hanging from a window – which was vandalised in June 2009.

Also in 2009, red paint was splattered across Banksy's Mild, Mild West artwork in Stokes Croft, Bristol, and repaired by the community group the People's Republic of Stokes Croft.

In

July, a Banksy image of a gorilla in a pink mask on the wall of the

former North Bristol Social Club, in Eastville, was mistakenly painted

over.

In

August a solicitor working on a thesis at Bristol University suggested

that Banksy works should be listed to protect them from vandals and

property owners. John Webster asked whether the works of Banksy should

benefit from such protection, given their cultural and financial value.