A graffiti artist has vandalised a Banksy image in Hendon in an apparent show of disdain towards his fellow spray painter.

Less than a month after the painting appeared on the wall of a substation at the junction with the A1 and the A406 North Circular Road, it has been defaced by another urban artist.

Before being targeted, the image depicted a boy seemingly marking the wall of a power station with the words “Last Graffiti Before Motorway”.

But over the weekend someone painted the word “PRICE-LESS” across the wall, with one national paper yesterday running pictures of him in action.

Some have suggested it is a protest by another artist who may believe Banksy has forgotten the “true meaning” of urban art following his success.

Members of the Banksy Forum website, which follows the artist’s work, have condemned the art attack, with one member saying the perpetrator is “jealous, and bitter”.

Another man, who calls himself buddings, responded to suggestions Banksy only carries out work for financial gain, by writing: “I don’t get this at all.

“Banksy wasn't paid to do it, he wasn’t hoping someone would sell the wall. Banksy could have done the same image on a canvas from the comfort of his studio for a massive amount of money but instead goes out in the middle of the night and gives London a little gift.”

He added: “How the hell does this remind Banksy of what urban art is all about?“

Forum member happy shopper said: “Obviously done by an idiot with no style at all.”

The substation is owned by Transport for London (TfL), who have previously said they are considering how best to deal with the artwork.