London's Westminster Council says a work by underground artist Banksy is graffiti and will be painted over.

The seven-metre tall work, painted in giant white letters on a concrete wall in April, was intended as a criticism of Britain's Big Brother culture and specifically the prevalence of CCTV cameras.

"One Nation Under CCTV", it screams, from a wall on which a CCTV camera is also mounted.

A child figure perched in a letter appears to be painting the message on the wall, which overlooks a post office yard in Oxford Circus.

The work, Banksy's biggest in London, was painted under the cover of darkness after the artist managed to erect three storeys of scaffolding behind a security fence, despite being watched by the CCTV camera.

But Westminster Council says the work will be painted over, The Times newspaper reported today.

The council says it will remove any graffiti, regardless of the reputation of its creator.

Banksy has no more right to paint graffiti than a child, the council said.

"If we condone this then we might as well say that any kid with a spray can is producing art," Robert Davis, the chairman of Westminster's planning committee, told The Times.

"To go and deface other peoples property is graffiti. Just because he's famous doesn't give him that right."

Banksy started out as a street artist, but his work is now coveted by celebrities and has earned him a lot of money.

In February, his Andy Warhol-inspired screen print of supermodel Kate Moss sold for $210,550 at a street art auction in London.

And a wall he had painted sold for $453,700.

Banksy's work has been bought by actress Angelina Jolie and singer Christina Aguilera.

- AAP