One of Banksy's most famous works has been defaced in what may be the latest episode of a long-running spat with a rival street artist.

The image above a shop in Bristol, which is generally accepted as the artist's home town, shows a police marksman with a child about to burst a paper bag behind him.

It appeared near Bristol city centre four years ago but has now been defaced with black paint. 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.

A key battleground has been a spot under a bridge on Regent's Canal in London where an artist said to be the mysterious and elusive Banksy painted over a section of a 25-year-old mural by King Robbo.

Robbo was thought to have retired but he – or perhaps someone else – emerged to partly restore the work.