Photographer Rat, a stencil and spray-paint work on a plastic road bollard from 2003 bearing Banksy's tag signature, will be offered at Lyon and Turnbull on September 27 (estimate £30,000-40,000) with a certificate from Vermin.

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Known as Vermin, based in New York and operating from the web address www.vermincontrol.us>, which was due to be launched last Friday, it will evaluate the authenticity of works that have been legally removed or salvaged from the street.

Previously, the sole body to issue certificates of authenticity for Banksy works has been Pest Control, which operates from the web address www.pestcontroloffice.com and is headed by Holly Cushing, who is closely associated with the artist himself as well as his primary dealer, Lazarides Gallery of Soho.

Because of Pest Control's close association with Banksy, some auctioneers will simply not proceed without a Pest Control certificate. These include Sotheby's and Dreweatts, who held their inaugural auction of urban art in London on June 17 where all the Banksy works were sold with Pest Control certificates.

However, Pest Control only deals with Banksy prints and gallery pieces, and as a rule rejects works deemed not originally intended for resale, such as street pieces executed by Banksy early in his career, and works that Banksy gave to individuals as gifts.

The official reasoning for this is that if Banksy or someone directly associated with him authenticated the street works, they would be opening themselves up to the risk of prosecution for vandalism. There is also an argument that works on the street could have been overpainted or altered by other graffiti artists.

Nevertheless, it is assumed in the art world that at least part of the reason for refusal is that Pest Control - and Banksy - does not want individuals cashing in on works that were intended for the street or as personal gifts.

It is not clear what Banksy and Pest Control make of the new authentication body.

Vermin is hoping its service will help restore faith in a market that has experienced significant uncertainty and in which fakes are common (In the run-up to their October sale alone, Dreweatts chairman Stephan Ludwig said he had come across approximately a dozen fakes).

Speaking in an interview with Artnet Magazine, an unnamed representative from Vermin said the board was "an entirely independent body acting in the interest of the collector", was "in no way connected to the artist", and would be "formed of a panel of established Banksy dealers who have been dealing since the early days in secondary-market Banksys".

Banksy works submitted to the board will have to meet certain criteria evaluated using "time-line" documentation, publications and photographic evidence. They will then be placed on a Salvaged + Saved register, an open resource website for individuals and organisations, for a one-month period, during which time counterclaims can be made and investigated.

If, at the end of that period, no valid counterclaim to ownership/authorship is revealed, the piece will be issued with a Vermin Certificate.

Asked about the rights of street artists over their own works, the Vermin position was clear: "There is no concern with the artist's rights in this situation. If he or she sprays or paints, leaving works out in the street, they become part of the public domain. Only the private owner of the surface it is painted on has rights over it. If that party then chooses to sell the piece and providing receiptage (sic) and reliable "time line" photographic evidence is supplied, then it gives its own validation," said the representative.

The first works with a Vermin Certificate to appear at auction will be offered in the September 27 Modern and Contemporary Art auction at Lyon & Turnbull in London. The sale includes five Banksy street works that have been authenticated by the Vermin board, including Photographer Rat from 2003, estimated at £30,000-40,000, a stencil and spray-paint work on a plastic road bollard bearing Banksy's tag signature.

Pointing to the shrewd practices of the new body, Lyon and Turnbull specialist Ben Hanly said the auctioneers originally had six Banksy works on offer, but one was withdrawn because Vermin could not authenticate it.