Back in 1980, Joe Strummer of the Clash introduced a live rendition of ''Brand New Cadillac,'' from the album ''London Calling,'' by announcing ''We're gonna do a song about something that no one here can afford.'' In those days, even a rockabilly cover had to be given a vaguely political or at least class-conscious spin: The Clash seemed to spring whole from the boredom and rage of the young British blue-collar milieu of the 1970s, which was both their source of inspiration and their intended audience.

This summer, the title song from that album resurfaced in the service of a rather different audience: potential buyers of a brand new Jaguar. In an extremely pervasive commercial pushing the Jaguar X-Type - a sleek four-door aimed at the ''entry-level luxury'' segment, and retailing for a relatively modest $30,000 or so - various urban go-getters imagined their city surroundings with a British makeover (complete with Jag, of course), while Strummer's throaty rumble delivered the simple message over a menacing guitar line: ''London calling.''

What was Jaguar thinking? Why does one of the most luxurious brands in the world want to go for a spin with one of the more aggressively anticapitalist bands of the punk era? As the advertising industry has gradually become completely entranced with the power of music, questions like this come up a lot. By now you could make a pretty good compilation of subversive music that's been used in ads, with selections from Lou Reed (''Perfect Day'' in a spot for the NFL), Iggy Pop (both ''Lust for Life,'' in a Carnival Cruises ad, and the Stooges song ''Search & Destroy'' in a Nike commercial for the 1996 Olympics), the Ramones (Bud Light once used ''Blitzkrieg Bop''), the Buzzcocks (Toyota), and even Creedence Clearwater Revival's scathing indictment of America's privileged class, ''Fortunate Son'' (repurposed by Wrangler). Again: Why?

Well, these things don't happen in a vacuum, and the answer is not that advertising ''creatives'' aren't sharp enough to know what these songs are really about. One explanation favored by cultural critics is that advertisers simply want to borrow a little of the rebellious feeling that many of these songs convey, and persuade their audience that buying, say, a luxury car is an attractively nonconformist act. It's also possible that advertisers spike their pitches with ''alternative'' references because it makes them feel hip. But probably it boils down to the simple fact that commercial-makers are clever enough to know that a song's ''real'' meaning doesn't actually matter. Where you or I might hear a counterculture anthem, there is also a collection of sounds and lyrical bites ready to be stripped for parts. From an ad-maker's point of view, even the most edgy rock 'n' roll is just so much musical wallpaper.

In Jaguar's case, the fancy car-maker and its agency had already settled on a summer-long US ad campaign underscoring the brand's Britishness and revolving around the words ''London calling,'' before the question of music was even addressed, according to Simon Sproule, vice president of communications for the company. The idea was that driving a Jaguar (which of course is a subsidiary of Ford) ''makes you British.'' Almost immediately, someone at the Irvine, Calif., branch of Jaguar ad agency Young & Rubicam suggested the Clash song.

So they tried it out on focus groups, and got a positive response: Apparently the tune, a seductively energetic number that is among the best the Clash recorded, sparked positive memories for many. ''Actually,'' Sproule contends, ''the people listening to things like this in the '70s are older now, and maybe they can afford a Jaguar.'' Moreover, the company has had good luck with other music-themed campaigns, which have used tracks by the Propellerheads and Sting.

Wasn't there any concern about a song whose words and music both evoke tension and doom, and seem to be warning of some vague class warfare or other apocalyptic calamity? ''The lyrics are strong,'' Sproule allows. ''But they're not offensive to anybody. They're strong and - angry.'' That's okay, though, because advertisers never use all the lyrics; they pick and choose. In this case, practically the only words we get are the song's title, repeated many times, and this one out-of-context snippet: ''London calling / yeah, I was there, too / An' you know what they said? / Well, some of it was true!'' In the song, after several verses laden with looming disaster, it sounds ominous and threatening.

But so what? In the ad, by itself, the lyric seems romantic and knowing - assuming you can even penetrate Strummer's accent. Chances are good that all most people come away with is the ''London calling'' mantra. Chances are also good that many people who own ''London Calling'' don't remember much more than the chorus. (And in fairness to them, even music writer David Quantick's 136-page assessment of the band, ''The Clash,'' calls the song's lyrics ''urgent, exciting, and to some extent meaningless.'')

While rock critics are fond of picking apart lyrics, and some highbrow types even think it's a good idea to collect them into books and call them poetry, most people don't listen that way. Viewers of that Wrangler ad no doubt recognize the guitar hook to ''Fortunate Son,'' and maybe pay attention to the only words from the song that make the ad: ''Some folks are born proud to wave the flag / Oooh, the red, white and blue.'' Maybe they forget that from there the singer makes it clear that he is not among those people, and that in fact he finds them vile. Or maybe they never knew what the song was about in the first place. Self-contained, the ad seems completely patriotic, and Wrangler must be happy with it, because it's been on the air for well over a year.

It's not just advertisers who find ways to lift a snippet that has a separate, stand-alone meaning. A few weeks ago on the MTV Video Music Awards, Rudy Giuliani made his entrance to the chorus from ''Rudie Can't Fail,'' yet another Clash number from ''London Calling.'' Those words by themselves sounded right, but as the spelling suggests, the song is actually a not-very-flattering meditation on Jamaican ''rude boys,'' slang for swaggering troublemakers. And ''London Calling'' itself also surfaces in the recent French film ''My Wife Is An Actress.'' When the heroine Charlotte Gainsbourg takes the chunnel trip from Paris to London, the tune plays, and seems meant to suggest that London is an exciting place where she will be sorely tempted to have an affair.

Despite all this, Sproule concedes that he knows there's grumbling among some Clash fans that using their music to peddle merchandise is an awful misrepresentation of what the band - which explicitly attacked ''the advertising world'' in the song ''Koka Kola,'' for instance - was about. (A spokesperson for Strummer's current label says he's not doing interviews about the Jag ad.) Some groups take explicit steps to avoid the dread appearance of commercial contamination, but this doesn't scare advertisers away. The famously lefty British band Chumbawumba sold the rights to the song ''Pass It Along,'' a musical brief for MP3 sharing, to Pontiac, and then turned their earnings over to a progressive activist network. Pontiac pronounced itself ''aware of'' (read: indifferent to) the band's politics, and ''very pleased'' with the spots.

Sproule doesn't sound too worried about the Clash's credibility with its audience. As it happens, the only time a Clash song ever hit number one in the United Kingdom was in 1991, long after the band had split up, when ''Should I Stay Or Should I Go'' was lifted by its appearance in a Levi's ad. (The same song has lately been part of a Stolichnaya Citrona spot here.) After all, Sproule points out, Jaguar even submitted story boards to the band's former members through Sony Music. They signed off on the campaign, he adds, ''and they know their brand better than we do.''

This story ran in the September 15, 2002 edition of The Boston Globe.