Switzerland's ambassador knew his country had an image problem. It was in the headlines for the wrong reasons, with the banks being accused of hanging on to Nazi gold, and he wanted to do something positive.

So Bruno Spinner invited some young graffiti artists into the embassy's underground car park and let them do what they wanted. They could even have a rave there a few days later, he decided.

The ambassador's rebranding exercise has had an extraordinary unintended consequence: one of the car park graffiti kids went on to become an artist collected by the rich and famous whose works command eye-popping prices at auction. The works at the embassy in London are by Banksy and are worth more than £1m. They are shown here and on the Guardian's website today for the first time.

There are about 10 pieces obviously by the Bristol-born artist. The most striking is a montage of 21 mohican-haired Lenins with the words "vulture capitalists" stencilled underneath. It is on the wall next to the car park exit and has suffered a few noticeable bashes - the consequence of tight underground car park corners.

Other works include a French poodle having a dream - or perhaps a nightmare - about a nasty-looking bulldog-faced poodle. Another has Mona Lisa with a green rifle sight on her forehead. Mickey Mouse is there too while one of the car park pillars has a threatening policeman and the words: "Laugh now, but one day we'll be in charge."

The Banksys, barring the odd flaking bit of paint, have held up well and have remained a secret known only to regular users of the car park

Spinner's idea was to get some of the UK and Switzerland's leading graffiti artists to spraypaint the walls and then have a rave once all the fumes had gone.

The party in 2001 was, a statement from the Swiss embassy said, "part of a series of events organised at the beginning of this century aimed to engage with the next generation of people and artists who will largely shape and determine the future".

The plan was to whitewash the walls but the embassy was pleased with the results and decided to keep the graffiti.

Switzerland's current ambassador, Alexis Lautenberg, said: "I was somewhat surprised when I drove in. The Swiss embassy obviously has many layers. This seems to be a particularly important and solid one and should be a source of inspiration every time you drive in or out."

Banksy has, remarkably, managed to keep his "they seek him here, they seek him there" anonymity throughout a career which has seen his fanbase widen and prices of his works rocket.

At Sotheby's in 2006 a stencil of a green Mona Lisa with paint dripping from her eyes sold for £56,700. Earlier this month a stencil of a sandwich-board wearing monkey called Laugh Now sold for £228,000 at Bonhams. Banksy's own view of these auctions is probably summed up by a picture he put on his website last year: "I Can't Believe You Morons Actually Buy This Shit," it said.

He also has many celebrity fans. Damien Hirst is said to collect Banksys. Angelina Jolie paid £200,000 for one and other stars such as Jude Law and Keanu Reeves have been reported as buyers.

The Swiss embassy can probably claim now to have the coolest car park in London so it was appropriate that last night it was used for the launch of the 2008 Your Game scheme, a charitable project run by the BBC and the Football Foundation to help young people who might be at risk of getting involved in gang culture, gun crime or substance abuse.

Caj Sohal, the project founder of Your Game admitted his jaw dropped when he saw the car park. "We agreed to go there not really thinking it was right but when you go in and see the quality of the work, it's a perfect fit for our project."