The xx act coy about the success of their astoundingly beautiful debut made “for the after-the-party party” to Laura Richards.

When asked for three words to describe the xx's music, lead singers Romy Madley Croft and Oliver Sim are confounded. It comes as little surprise that they struggle with this conundrum. “Melancholic and uplifting” are two contrasting words often associated with the oxymoronic four-piece from South West London, and the group cite contemporary r'n'b and the likes of The Cure, The Kills and Pixies as their biggest influences. They really are quite a puzzle. But there is no question or confusion when it comes to the success the band have witnessed in the last few months.

“I'm sure once we do stop I'll kind of freak out a little bit, take it all in. But yeah, it's been good, really good,” gushes Oliver.

The last few months have seen them appearing on Later with Jools Holland, supporting Florence and the Machine at venues as renowned as Shepherds Bush Empire and filling the Festival Republic tent at both Reading and Leeds.

"Well that was just a shock. We were on at two and we thought everyone would have a hangover," says Romy. "When we walked out on stage the tent was full and actually the crowd were really responsive and so it was amazing," adds Oliver.

The xx formed during their GCSE music studies at a school whose alumni includes Hot Chip, Burial and Four Tet, but Oliver, Romy, Baria and Jamie had already started making music together before they had heard of these artists.

"The school's claim to fame was Pierce Brosnan," laughs Oliver. "I stole my sister's CDs and she was listening to a load of '90s American r'n'b. So we're into a lot of people like Aaliyah, Missy Elliot, TLC, Lauryn Hill and Ginuwine."

Sim would share his steals with Croft, his friend since childhood. They enjoyed the melodies especially, which is quite audible in their soft-spoken harmonies on debut album xx. Oliver and Romy are very modest when grilled about the sterling reviews of their debut album and it seems Oliver feels the great write-ups may almost deter listeners.

"I know sometimes I can react quite strangely to some really quite good reviews. With a band being forced on me in a way I can kind of not want to like them, but with such nice things being said it's more flattering than anything really."

Romy seems pleased just to have some feedback from people other than family members. She and Oliver both laugh approvingly when told that the Observer described xx as an album crafted for a come-down.

"I quite like that. I'm happy with it being for the after-the-party party."

It certainly seems that the xx aren't your average young band, and their recent stint as Florence and the Machine's support act saw them somewhat shy away from the rock and roll lifestyle of their peers.

"It's quite hard to keep up. We're all quite chilled as a band; we don't go out and seek the party afterwards. We just chill out when we do a gig."

Taking this minimal approach was a stroke of luck when it came to establishing their musical idiosyncrasies.

 After working with acclaimed producers Diplo and Kwes, the band chose to self-produce xx. Oliver claims that although working with these producers was a valuable experience, they wanted to preserve the insular purity of their record by producing it themselves.

"Jamie's in the band, he knows how sounds should sound, we have no problem saying stuff to him and he has no problem saying 'that sounds crap, sing that better, do that better.'"

What is perhaps most interesting of all is the choice to use electronic drums in both performance and on record which, according to Romy and Oliver, gives fluidity and spontaneity to their live performances. 

"If we want to play on for an extra verse on a certain bit, we can, whereas with a backing track you don't really have that option," says Oliver.

It's tangible in their live performance - on 'Islands' the group drift up and down in tempo, and 'Infinity' feels like it could go on for just that, with the climax continuing beyond the length on record.

Looking to the future, the band dream of gigs at the Natural History Museum, Brixton Academy and on the beach at dusk, a trajectory that it seems their success will naturally facilitate. After much deliberation Oliver and Romy finally decide on three words to describe their music: "Dark, laid-back, and pop!" Three simple words for an unassumingly complex band.