A bizarre building with some pretty good art attached

Charles Darwent seizes a rare chance to step inside the London Ark

Anyone agonising over which of the venues to ogle in London's forthcoming architecture-and-heritage Open House weekend might like to add one of the less likely contenders to their list: the Ark, that ill- starred brick whale beached on the wasteland between the Hammersmith Flyover and the tube line to Heathrow.

There are three good reasons for making the pilgrimage to this nook of urban grime. First, the Open House programme offers a rare chance to see inside what is actually one of the most brilliant pieces of British architecture since the war: the septuagenarian swansong of the much under-rated Ralph Erskine.

For all its ecological high-mindedness - part of the Ark's visual oddity stems from Erskine's determination that it should be run without guzzling fossil fuels - the brick whale is actually rather a selfish building. Its copper-coloured carapace, usually viewed from a speeding car, gives no hint of the extraordinariness inside it: part Alvar Aalto, part Corb-goes-to-Ronchamp, and altogether triumphant.

The second reason for hiking out to darkest W6 is the collection of art which the Ark's tenants - the transnational drinks giant, Seagram - have been quietly accumulating over the past two years. Corporate art collections tend not to be objects of joy. At worst, they are the playthings of chairmen's wives; at next-to-worst, they are over-literal reflections of their creators' businesses. (Paintings in the Cable & Wireless collection are, notoriously, mostly of cables and wirelesses.)

Seagram's collection shows rather more finesse in this regard. According to Jill Preston - one of a triumvirate of employees charged with putting it together - there is a double agenda behind the artworks in the Ark: to respond to the architecture of Erskine's cetacean masterpiece, and to challenge Seagram's staff members to "think outside the box".

Challenging the Seagram collection certainly is. Among the works commissioned specifically for the building is an installation by the Scottish artist, Ian Hamilton Finlay, entitled Sea Flower. Painted on the roof of one of Erskine's rocky outcrops, Sea Flower is visible only from the elevated walkways that form the whale's ribs. The picture's inaccessibility is apposite enough: to describe Hamilton Finlay's work as being in any way approachable would be an error. Sea Flower consists of a collection of call-signs from Scottish trawlers, painted in a circular maze of white lettering on an ultramarine background. What Seagram's employees make of it is not a matter of record. Nor is it really the point. The important thing, by Preston's reckoning, is that they are asked to make anything of it at all: to furrow their corporate brows as they walk over it.

Nor is Sea Flower by any means the most opaque of the works in the Ark. David Cheeseman's installation, Lung - also the result of a specific commission - is a three-storey recreation of a pair of human lungs, made from anodised grape stems and fixed to the wall of a tower, the East Drum, which rises through the Ark's eight galleried floors.

Employee participation in the Lung's creation extended beyond mere brow-furrowing. Cheeseman's several hundred grape-stems were provided by Seagram's workers, all chewing manfully in the name of art. But Lung is visceral in more senses than one. The work's grape-stem bronchia can be read in a number of ways: as a response to Erskine's architectural breathing-space, or (Seagram's traditional business being largely vinous) as an allusion to the provenance of the money that made it all possible. Whichever reading you choose, though, one fact is beyond debate. The work, like Hamilton Finlay's Sea Flower, is site-specific, and not simply in terms of its geographical location.

If this seems an obvious point, it nonetheless provides the third reason for visiting the Ark a fortnight from now. On 26 August, John Prescott ruled that the US publishing group, Time & Life, would have to return works of art - notably a reclining nude by Henry Moore - originally commissioned in the 1950s for its Bond Street offices to the premises in question. This was not entirely the triumph of Labourite rectitude over capitalist greed it seems. Time & Life had not tried to sell the Moore: they had lent it to the National Gallery of Modern Art in Edinburgh, where it had been seen by three- quarters of a million people. Prescott's ruling means that the sculpture will be returned to a private office block where it will be seen by no one (or no one from the public), even on Open House weekends.

Political irony is not the point of this story, however. The question is what effect Prescott's new role as a champion of site-specificity will have on patrons who now face having to leave the fruits of their corporate largesse behind them when they move. Seagram's European president, Martin Frost, notes that the budget for art in the Ark ran to "hundreds of thousands rather than millions of pounds": should he be forced to leave Cheeseman's Lung inside Erskine's ivory tower, says Frost, he would simply tack its value onto the cost of the ensuing lease. This may be a touch optimistic. Whether a prospective tenant will really find the idea of having to pay for an artwork which is not simply deeply quirky but has been masticated by the employees of his predecessor financially beguiling is open to doubt.

The upshot of this may be gloomy. According to Jill Headley, director of the quasi-public Contemporary Art Society Projects and one of the people who advised Frost on his collection, the danger is that corporate patrons will in future spend less and play safe. "My worry is that people may start looking for the lowest common denominator," says Headley. "Buying dreary, compromised work that won't frighten the next tenant and which companies won't mind leaving behind them." If she is right, then daring, intelligent corporate collections like the one in the Ark may become things of the past: another reason picking your way under the Hammersmith Flyover come Open House weekend.

Open House: 19 & 20 Sept; information on 0891 600061. Official guides to the scheme are available from from local libraries and tourist information offices. Visitors to the Ark are asked to pre-book on 0181 348 3109.