The group formerly known as Exit Through the Gift Shop receives an unexpected reward for acceding to graffiti artist's request

The painting arrived outside Simon Duncan's west London home inside a battered old van. Overnight it has put him at the heart of street culture and made him £200,000 wealthier. The new work by Banksy was sent unexpectedly last week to Duncan, a 41-year-old web developer, as compensation for the world-renowned graffiti artist having coincidentally chosen the name of Duncan's band as the title for his film, Exit Through the Gift Shop.

"I am a drummer in a band that was called Exit Through the Gift Shop that I started with friends 18 months before I turned 40. It was a kind of midlife crisis, but we are still going, with a different line-up, and it has become a bit more serious," said Duncan, who agreed to change his band's name to Brace Yourself in an arrangement with Banksy.

"We had these hilarious emails from someone saying he was Banksy, but we didn't know if they were genuine," said Duncan. "Then a scruffy white van arrived. The driver had no idea what he was carrying."

The band plan to unveil their new name and backdrop, which shows the grim reaper riding a dodgem car, at a London gig this week.

"When we saw the painting we could not believe it," said Duncan. "It is the size of a double bed, for a start. We had to insure it, so a man from Sotheby's came over to see it in my loft. He said to me, 'This is surreal. I have just been valuing an 18th-century portrait in a stately home, but it is not as valuable as this.'"

The band have put the painting in storage at Sotheby's and will perform in front of a full-size copy.