'Official' tag for Banksy works

'Gangsta Rat' is expected to fetch between £25,000 and £35,000

Works by graffiti artist Banksy are to go under the hammer accompanied for the first time by a certificate of authenticity.

Edinburgh-based auctioneers Lyon & Turnbull will sell five "street pieces" at their forthcoming sale in London.

A board has been set up to provide an independent authentication service dedicated to these early works.

The move was driven by a contemporary art market concerned that fakes do not end up in circulation.

Ben Hanly, head of modern and contemporary art at Lyon & Turnbull, said the new authentication board - known as Vermin - would address a grey area in the market.

A committee called Pest Control was set up within the past few months to authenticate Banksy's prints and canvasses after fakes began to appear on the market.

The market is relatively small for street pieces as not many have survived, even though they are by far the most important Ben Hanly Lyon & Turnbull

But the body, which is endorsed by Banksy himself, deliberately avoids handling his "street pieces" created without permission early in his career.

Neither Banksy nor anybody directly associated with him is free to authenticate these works without the risk of opening him up to prosecution for vandalism.

But now, if authentication can be proved by documenting the work's proven history, it will be given a Vermin certificate. All works and their provenance would then be available for public examination and published on the internet.

It is hoped the process will help protect against future fakes and will provide a comprehensive guide to surviving works.

Mr Hanly said: "They want the certificate to be absolutely rock solid.

"The market is relatively small for street pieces as not many have survived, even though they are by far the most important. They're basically where his entire style came from and where his career came from."

Five street pieces valued at between £25,000 and £150,000, and a range of early prints, will go on sale at Lyon & Turnbull's auction of modern and contemporary art in London on 27 September.