The X Factor winner has now sold 897,000 copies and already has the fourth best-selling debut single for an X Factor act, behind only 2008 winner Alexandra Burke's 'Hallelujah' (1.2 million), 2005 winner Shayne Ward's 'That's My Goal' (1.1 million) and 2010 winner Matt Cardle's 'When We Collide' (1 million).
'Impossible' has now overtaken 'Gangnam Style' to become the fifth biggest selling single of 2012.
will.i.am and Britney Spears climb one place to two with 'Scream and Shout', while Psy's 'Gangnam Style' climbs up to three, with both selling over 110,000 copies each.
Olly Murs and Flo Rida climb up three spots to four with 'Troublemaker', while the Christmas number one 'He Ain't Heavy He's My Brother' by The Justice Collective drops four to five.
Bruno Mars drops one place to six with 'Locked Out of Heaven', while Taylor Swift climbs one spot to seven with 'I Knew You Were Trouble'. Rihanna is back up two to eight with 'Diamonds'.
Robbie Williams rises five places to nine with 'Candy', while Labrinth climbs one place to 10 with 'Beneath Your Beautiful'.
The Script rise 17 places to 17 with 'Hall of Fame', with Maroon 5 climbing 13 to 18 with 'One More Night'.
Sam and the Womp's 'Bom Bom' is one of a number of re-entries in this week's top 40, rising to 39.
Flo Rida's 'I Cry' climbs 38 places to 40, while there are also re-entries for Little Mix's 'Wings' and One Direction's 'Live While We're Young' at 36 and 38 respectively.
Carly Rae Jepsen's million-seller 'Call Me Maybe' also leaps 23 places to 33.
Taylor Swift also re-enters at 24 with 'We Are Never Ever Getting Back Together', while Jay-Z and Kanye West land at 37 with 'Paris'.
Watch the video for James Arthur's 'Impossible' below:
Source: Official Charts Company