They're a dance band you can't dance to, a hip young group more popular with the middle-aged than with their own peer group and - strangely, for a multi-million selling group - immune to that pop-wide epidemic, narcissism. They make no bones about their odd way of working - he writes the tunes; she listens, she writes the lyrics: they rarely meet. And self-promotion is hardly their strong suit. Take this story: when Portishead made their long-awaited comeback with new material after a three-year gap, they did a showcase in New York and, when a huge-selling, monthly rock music magazine asked for a photo so they could put them on their September front cover, the band replied that they "couldn't be arsed". Named after the tiny town outside Bristol that they come from, the band is basically rock/dance music's odd couple. There's 24year-old hip hop, techno whizzkid Geoff Barlow who does all the music, and there's the "a bit older" Beth Gibbons, who never really got into dance culture but likes Janis Joplin and torch singers, who write such heartbreak lyrics.
A few years back and both on the dole, they found themselves together on a job-creation scheme and, discovering a mutual interest in music (albeit at different ends of spectrum), formed Portishead.
Their debut album, Dummy (1994), was a revelation, sold millions of copies and won the Mercury Music Prize. Cleverly, they had taken the contemporary hiphop sound, slowed it down, renamed it trip-hop (or "tranquilised hip-hop") and got Beth to do her best Billie Holliday/Edith Piaf vocals over the music.
By turns slow, sinister, sad, and sexy, the Portishead sound moved from the underground clubs to the mainstream dance charts, and then crossed over not just to the rock charts but to the dinnerparty/fondue set who discovered that "unlistenable youth music" could indeed be the perfect replacement for the usual postprandial soundtrack of Ennio Morricone and Michael Neiman. Big in Dalkey? You betcha.
The first album sounded like a soundtrack for an imaginary film, shot through as it was with all sorts of spookily atmospherics moments and cut-up, fade-in, fade-out echoes of clubland rhythms. It also rehabilitated the use of the obscure musical instrument the Theramin, a sound very big in the 1950s - it was used to denote that "aliens" had landed in cheesy sci-fi movies: it was also used a lot by the Beach Boys. Once Dummy went to the top of the charts, sales of the Theramin increased by 500 per cent.
Despite being drolled over as "zeitgeist-moulders" and "genresmashers", Geoff and Beth stayed enigmatically aloof from the media frenzy that greeted their arrival. Very country-yokel in manner, they just smiled placidly and said "that's nice" when the compliments rolled in.
But the band ran into the difficult-second-album syndrome, as Geoff explains: "I thought the second album would happen straight away, but the reaction to the first album was such a shock to us . . . Despite everything, and all the money, we tried to be very sensible about the new album - we went into the studio every day, except weekends, there was no larking about or time-wasting and we even banned booze from the studio, I even banned the use of instruments which we had used on Dummy."
But the sort of perfectionism that gave Geoff an ulcer when he was only 22 made the studio sessions fraught and had the record company on the phone wondering when the new album would be ready - not least because the new album came in four times over budget, what with orchestral strings costing £30,000 a day. So the band took the predictably unpredictable step of scrapping a year's worth of work and starting again.
"I had lost it," Geoff says. "I had turned to jelly with the pressure.
"I wanted the album to be different, so I made lots or rules about what to do and not to do and it took Beth to say to me, `look, just enjoy yourself' . I would say `all my ideas are crap!' and she would say `OK, let's hear the crap. I'm sitting here waiting to sing something, we'd better get something done before we die of old age'. It soon became not so much the `difficult second album' but the `bloody impossible second album'.
"But then I started to share the responsibility around and as a result we got it recorded and now the balance in the band is much better."
Three years on, the album (called, confusingly enough, Portishead) is ready and true to form Geoff is shouldering all the media/marketing responsiblities with Beth nowhere to be seen. "We have a deal: I do the interviews and she'll have the odd photo done, but not too many - she calls it her penance.
"I don't like to speak for Beth," he says, "because I really don't know what goes on inside her head.
"The truth is, she doesn't want to talk about her singing or her lyrics. I don't think she would be comfortable with it all. Even when we work, it's a strict split between the music and the lyrics. I send her tapes, she'll put her vocals over the top. I feel a lot closer to her now than I did doing Dummy: then, I was so into making an album I didn't stop to find anything out about her personally. Since then, we've socialised a bit more and luckily we get on. But the media think she is trying to create this mystique when she's not. What can I tell you? She's a very insular, shy person."
Who cares what she's like? She sings like an angel. Albeit a slightly drunk, chain-smoking and heart-broken angel.
Portishead's first new work for three years, a single called All Mine is released on Monday with the album to follow on September 29th.