Investors who banked on Banksy

A work by graffiti artist Banksy, bought for £700 seven years ago, could sell for up to £500,000 at auction.

The "corrupted" oil painting, showing a military helicopter stencilled over an original painting of a tranquil seaside scene, is the star exhibit in a show of urban art that opens tomorrow at Selfridges.

Its owner, described only as a "lucky investor", bought the piece at an auction at London nightclub Cargo.

The work is one of a series of " vandalised" oil paintings produced by Banksy over a five-year period. Another, entitled The Rude Lord and featuring a 1776 Thomas Beach portrait altered to reveal an extended finger, sold for more than £300,000 at auction last year.

Mary McCarthy, of auctioneers Dreweatts, which will sell the paintings, said: "This is the first corrupted oil Banksy ever created. He did a number of them but because he doesn't catalogue-his work it's difficult to tell how many. He tended to choose rather twee, chocolate-box paintings and put his mark on them. This one has his helicopter-a well-known Banksy hallmark, so it's fairly special. It will be interesting to see what it goes for."

Six other original Banksys will appear in the exhibition. They include Glastonbury Sign, a stencil spray on foam board depicting a policeman lighting a young girl's cannabis joint, and Portrait Of An Artist, an oil on canvas.

Ms McCarthy said: "These pieces have been in private collections. This is a unique opportunity for members of the public to view some pieces that are very fresh to the market."

The exhibition also features the work of 45 other urban artists, including Paris-based Blek le Rat.

Ms McCarthy said: "It's a really great overview of street art from its emergence in New York to the present day."

The preview will run until 1 June and the majority of the pieces will be auctioned at Village Underground in Shoreditch on 17 June. Banksy's helicopter painting will not be sold until a second auction in October.

ALSO IN THE SALE

Glastonbury Sign, 2003

Stencil spray paint on foam board

Guide price: £30,000 to £50,000

Presented to the present owner at Glastonbury Festival in 2003. It was stored behind the owner's sofa for five years.

Untitled, 2000

Acrylic and stencil spraypaint on canvas

Guide price: £25,000 to £35,000

Presented by the artist to its present owner. Hung on wall of Ether Bar, Bristol, before being taken to a private house

Bombing Middle England

Spraypaint on board

Guide price: £50,000 to £80,000

Submitted for auction by Banksy's agents, Pest Control

Watch Tower

Acrylic on olivewood sculpture

Guide price: £6,000 to £8,000

By Banksy and Kelsey Brookes. Was in his 7007 Bethlehem exhibition, Santa's Ghetto

Portrait Of An Artist, 1999

Oil on canvas

Guide price: £150,000 to £200,000

Bought by a collector in 1999 for £200 at one of Banksy's first exhibitions

Laugh Now But One Day We'll Be In Charge

Acrylic and stencil spraypaint on paper

Guide price: £30,000 to £50,000

A rare early piece