When you think of One Direction songs, which do you envisage being the band's biggest selling? Any idea? Well, One Direction fans, it's time to stop squabbling because we have the official list right here. We're not talking about One Direction's Best Song Ever, we're talking about the biggest selling.

Well, it's actually the Top 20 biggest selling songs on the Amazon UK MP3 Music Store but we'll be willing to stake a considerable amount that it echoes the elusive list of overall biggest selling One Direction songs. For the record, the good people at Amazon were the only people who would provide us with the figures. So well done them.

20. They Don't Know About Us

One Direction Premiere

We're starting on a positive note with number 20 'They Don't Know About Us'; a song about being madly in love despite being so young, and that ever familiar feeling that you're absolutely sure there's no relationship like yours going on in the world. Taken from their second album, it has been written by country producers Tebey Ottoh and Tommy Lee James, and thus has a rather a different vibe about it than some of their other hits with a piano led intro which continues as a gentle backdrop throughout the rest of the song.

19. Nobody Compares

One Direction This Is Us Premiere

'Nobody Compares' is another of those One Direction songs that failed to make the tracklist of 'Take Me Home' but appeared on the limited yearbook edition and iTunes Store deluxe (as well as the Japanese versions of the two). It reached number 174 in the UK chart and 79 in Canada and is a pretty heartfelt tune about been dumped by a girl without warning. That's the beauty of 1D though, they're never afraid to pick up on those timeless topics people love to write so much about.

18. I Want

One Direction red carpet

McFly's Tom Fletcher returns as a writer for 1D with 'I Want' which featured on the tracklist for 'Up All Night'. It's got quite a unique retro edge to it and tells of men's frustrations with the materialism of the women they're dating. It's perhaps a little sexist, but for a band so often compared to the biggest selling artists of the world, The Beatles, it's hardly an issue for most fans. Richard 'Biff' Stannard and Ash Howes produced the track.

17. I Should Have Kissed You

One Direction on stage

One Direction seem to only have one thing on their mind; 'I Should Have Kissed You' is the first of three songs from their first two albums to mention kissing in the title (though it's not to be confused with the song of the same name by Chris Brown). This is from 'Up All Night' and was produced and co-written by Steve Robson alongside Norwegian songwriter Ina Wroldsen.

16. Heart Attack

One Direction live

Another One Direction song about heartbreak, 'Heart Attack' just scraped the Canadian Top 100 chart at number 100 on its release on their 'Take Me Home' album. However, in true 1D form, they still manage to turn a sad subject into an upbeat sing-a-long tune with a little essence of Michael Jackson thrown in there with the repeated 'Ow!'s that one of the songwriters from the album, Savan Kotecha, mentioned was mainly courtesy of Niall.