Is this Banksy at work?

This picture is believed to be the first showing Banksy at work.

The maverick street artist has kept the public guessing over his identity despite his creations now selling for six- figure sums to Hollywood stars such as Brad Pitt and Angelina Jolie.

Several photographs of the Bristol-born artist - real name thought to be Robert Banks - have emerged in recent years claiming to unmask him. But the latest appears to have caught Banksy creating one of his trademark murals on the side of a building in Bethnal Green.

A passer-by took several pictures on a camera phone at Pollard Street near the Bethnal Green Working Men's Club. They show Banksy with an assistant using scaffolding and a truck. The finished work depicts a disgruntled street worker resting after painting a double-yellow line which turns into a flower.

A recent auction of 10 pieces of Banksy art sold for more than £500,000 at Bonhams.

With his anti-capitalist and anarchist images of giant rats and other animals, the artist has cultivated his anonymity to allow him to pull off a series of stunts, including releasing an inflatable Guantanamo prisoner doll at Disneyland last year.

The latest work may have been a riposte to Tower Hamlets council, which has vowed to erase all of Banksy's work. A spokesman for the artist confirmed the artwork is genuine but refused to confirm whether the man in the photograph is him.

"We never confirm or deny whether an image shows Banksy," said the spokesman. Shortly before the Bonhams' auction Tower Hamlets councillor Abdal Ullah said: "Graffiti is a crime. It spoils the environment, makes our neighbourhoods feel less safe, and costs thousands of pounds each year to clean - money that could instead be paying for local services."

Hackney council, which has a high concentration of Banksy's work, has taken a similar stance and already cleaned some away.

"We can't make a decision as to whether something is art or graffiti. The Government judges us on the number of clean walls we have," said a Hackney council spokesman.

When one of Banksy's artworks - stencilled on a wall in Bristol - came under threat, a public vote showed that 97 per cent wanted it to be kept.