The graffiti is not tagged

The spray painting opposite the Children's Hospital is of a crouched armed police officer, with a child about to burst a paper bag behind him.

Nearby workers said they had noticed the graffiti on Monday.

Hospital fundraiser Laura Denson, 26, said: "I think it's real. People rip him off but it looks authentic. We like it."

"[It] is very likely to be by Banksy as the style of the work is the same as what has been previously published and I have previously seen," added Jon Evans.

No signature

Staff in the hospital fundraising office have e-mailed Banksy's website asking if they can auction off the work, but have yet to receive a reply.

A suspected counterfeit Banksy was recently removed from an area near the Triangle in Bristol, prompting suggestions that a counterfeit "Pranksy" artist was operating in the city.

Councillor Gary Hopkins said: "My own view is that [keeping any counterfeits] would depend on how funny they are."

The graffiti opposite the hospital is not tagged with Banksy's trademark signature.

The artist, born in Yate, has become something of a cause celebre amongst celebrities, with his work fetching hundreds of thousands of pounds at auction.

He was even exhibited recently alongside pop artist Andy Warhol.

And an e-petition on the 10 Downing Street website asking for his original work to be preserved has collected more than 200 signatures.