The trio's collection beat David Bowie on the format's year-end charts to claim the top spot, after releasing the album back in September.
Bowie landed at two with his 1972 classic record The Rise and Fall of Ziggy Stardust and the Spiders from Mars, reports the Official Charts Company.
Jack White's Blunderbuss - which was the best-selling vinyl in the US during 2012 - lands at three, while Adele is at four with 21.
Overall vinyl sales increased for a fifth year in 2012, with a total of 389,000 units sold across the 12 months. The feat means sales of the format were up by 15.3% on 2011's sales of 337,000.
"With more than 60 years of loyal service, the vinyl LP is by some margin the most enduring album format of all time," said Geoff Taylor, BPI Chief Executive.
"Although sales overall are small compared to CD and digital albums, vinyl's collectability and appeal to audiophiles is drawing in new fans, in particular through initiatives like the popular annual Record Store Day.
"Increasingly LPs also include codes that can be redeemed online for digital albums - giving fans the best of both worlds."
Travis's 2001 album The Invisible Band remains the 21st Century's best-selling vinyl, having sold 28,700 copies to date.
The Top 10 best-selling vinyls in the UK during 2012 are as follows:
1. The xx: Coexist
2. David Bowie: The Rise and Fall of Ziggy Stardust
3. Jack White: Blunderbuss
4. Adele: 21
5. Tame Impala: Lonerism
6. Bob Dylan: Tempest
7. Beach House: Boom
8. Alt-J: An Awesome Wave
9. Drive-By Truckers: Go-Go Boots
10. Pink Floyd: The Wall
Photo gallery - albums to be excited about in 2013:
Copyright: PA Images Ian West/PA Wire/Press Association Images