The organisers of a spoof British art competition claim they have caught the guerrilla artist Banksy trying to out-spoof them.

The judges of the annual Turnip Prize were far from impressed by a professional-looking entry they suspect came from the secretive Bristol graffiti artist. Under the strict entry criteria for the pastiche competition the artists must have spent as little time on their work as possible.

Suspicion has mounted about the identity of the artist since the artwork was dumped outside the New Inn pub in Somerset. The pub has been running its own annual art prize as an antidote to the “pretentious” Turner Prize since 1999.

The anonymous entry bears all the sardonic hallmarks of Banksy, the anonymous street artist whose work now sells to wealthy collectors for hundreds of thousands of pounds.

The painting shows a stencilled Mona Lisa firing a turnip from a bazooka. The rocket-launched vegetable is shown flying over a seaside pier below the word ‘Banksea’.

The scene has been painted onto a traditional seaside caricature board with cut-outs for day-trippers to place their own face through.

Banksy’s publicist, who claims never to have met the artist, was unavailable to confirm whether he really had entered the contest.

The graffiti artist, whose real name is believed to be Robert Banks, was captured on camera for the first time in The Times last month. He has kept his true identity a secret despite becoming infamous for a number of artistic pranks.

The British Museum took eight days to realise that Banksyus Maximus, a rock depicting a stone-age hunter with a shopping trolley, was not a genuine artefact.

Banksy also painted a hole showing an idyllic blue sky on the Palestinian side of the West Bank wall and the sneaky artist has applied his distinctive touch to hundreds of ordinary walls across Bristol and London.

Brad Pitt and Angelina Jolie are among his growing array of fans, after reportedly spending more than £1 million on his works at a sale at Lazarides gallery in Soho this year.

If the entry submitted to the Turnip Prize is genuine it would be worth tens of thousands of pounds, but the debate over authenticity is of no interest to the judges. Whoever painted it stands no chance of claiming the annual prize.

Trevor Prideaux, the organiser of the event, explained how the winner would be selected: “It is awarded to the person who has created something that they perceive to be crap art using the least amount of effort possible.

“It does seem to be in Banksy’s style and the fact it was left anonymously on my doorstep does add to the possibility that it could well be one of his.

“But we do disqualify those who are perceived to have used too much effort. Someone has thought too much about this one and tried too hard. So for that reason it’s not likely to win. The odds are very long on it.”

Judges will gather this evening for the first round of the selection process. The competition has been running for eight years since Mr Prideaux took umbrage with the Turner Prize, won that year by Tracy Emin and her unkempt bed.

The winner of the trophy, a turnip nailed through a plank of wood, usually ends up in the hands of the entrant who has spent the least amount of time on it.

In 2003 that honour went to James Timms, whose work "Take a leaf out of my chook" constituted a raw chicken stuffed with leaves.

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