But then Sub Pop's 20th-anniversary festival in July 2008 brought Eugene Kelly and Frances McKee together again, officially, as The Vaselines. That event kicked off a collaborative reunion that many thought would never happen, not least the principals themselves.

"Two years ago, when we did the Sub Pop festival, someone asked us if we would ever make another Vaselines record, and we both said, 'Absolutely not,'" says McKee. "You know, we weren't going to do it, and here we are, we've done it."

Asked what about 2010's musical landscape makes it the right time to have another go at The Vaselines, McKee shrugs off the question. She's clearly been asked this before, leaving the impression that there's been some prior insinuation behind it — as if more cynical elements have assumed that The Vaselines' reunion is not much more than a well-planned marketing ploy.

"I don't know if it is the right time," she admits. "We don't plan anything, that's just the way it happened. We didn't have a big, cunning plan for the last 20 years. I'll tell you what we did. We got my astrological track, and we got Eugene's astrological track, and we waited for the exact moment for the two planets to collide."

McKee speaks wryly, with a sparkling lilt in her voice; her Scottish accent makes everything seem just a trifle more charming than perhaps it would otherwise. In reality, The Vaselines' reunion seems to have been more of a "hey, why not?" moment than anything else.

Over the years, Kelly and McKee kept in contact and even collaborated on the odd gig, though never in anything approaching an official capacity before this. McKee helpfully explains how the whole thing got started.

"In 2006, I put out a solo album," she begins. "I did a few shows, and was looking for someone to open for me. My friends suggested Eugene, and I didn't think he would, but I phoned him up anyway to see if he'd be up for it. When we did that, we played a few songs — you know, just guitars, no drums or anything, but we played a few Vaselines songs, and it went on quite well."

"Then the following year, my brother-in-law organized a charity event for my sister," McKee continues. "Eugene and I were going to play at it, but just a solo-career thing, and then my brother-in-law asked me if we were going to play some Vaselines songs, as well, and I said, 'Yeah, probably.'"

"Eugene phoned me up and said the guys from Belle and Sebastian are having sort of a bit of a break, and they'd be keen to play guitar and bass and drums. I thought, 'Why not try it?' I didn't really know them that well — I didn't know them at all, in fact — but Eugene's really good friends with them.

"We went and did a rehearsal, and it was great. At the same time, Sub Pop had asked us to do their festival, and we had told them originally no. Then we thought, 'It's such an occasion, why not,' and that's what happened."

Apparently, things went on quite well at the Sub Pop show. That was when McKee and Kelly decided it was high time to record another Vaselines album.

Sex With An X, released about a month ago, is an interesting reflection on the band. It sounds strikingly familiar, yet also strangely foreign.

Stripped to its essentials, it's pure Vaselines: Simple song structures and sing-along choruses; that wonderfully disjointed blend of lascivious material and coquettish delivery that permeates virtually all of the duo's material; the exuberant irreverence that somehow manages to skirt the line of actual offense; the near perfect interplay of Frances and Eugene's less-than-perfect vocals.

It's not something The Vaselines would have recorded 20 years ago, though.

"No, I don't think so," agrees McKee. "I think 20 years ago, I had probably used up as much of the songwriting ability as I had at that stage. I could never have written what we've written now, 20 years ago. Not that it's that much different in many ways."

"Even the person who mastered it said, 'That just sounds like The Vaselines,' and that's what everybody has said, when you hear it, so that's been real good," she says.

However, "It's not been our intention to make another 'Monsterpussy' or anything like that, because it is quite different, but it is Eugene and I," McKee adds. "All the songs are pretty upbeat, and there's just a dynamic there that shines through, I think."

That McKee would choose what is likely the band's most ridiculous, over-the-top, functionally perverse song as an example of the differences between The Vaselines then and now truly does capture the scope of how the band has changed. In short, they're not twentysomethings anymore, but fortysomethings with lives very much different from the carefree lifestyle represented so effortlessly by the band's first go-round.

Maturity has been gentle on The Vaselines, but has left its mark on their music as surely as on their faces, which have retained their youthful vibrancy yet shed the baby-faced naiveté etched in the expressions of their first few years as a band.

Silliness is replaced by a wry, knowing humor; deliberate simplicity has taken the place of inherent clumsiness; polish stands in for immediacy. Not all of these are good changes, but they are understandable.

What's sure is that The Vaselines aren't trying to be anything other than what they are. McKee even brings her children to gigs when the band plays in Glasgow.

"My eldest, he's only nine, but he loves it," she says. "He's really into a lot of different music, but he did tell me the other day that he prefers Nirvana's version of 'Molly's Lips,' and in front of the band, no less, so he's getting it now!

"He did say, 'Mom, I do like your songs; I just put them on my iPod.'"