The singer's double A-side single 'Evergreen' and 'Anything Is Possible' was released in February, 2002, and went on to sell over 1.8 million copies in the UK, reports the Official Charts Company.
Reacting to the news, the star tweeted: "Ten years ago I won Pop Idol. Since then I have still not achieved my dream of a Tupperware range. Life can be cruel..."
Young managed to fend off competition from Adele's 2011 hit 'Someone Like You', which landed at two with sales of 1.35m. Gareth Gates is at three with 'Unchained Melody', which shifted 1.34m units.
Maroon 5's 'Moves Like Jagger' is at six, Kings of Leon are at nine with 'Sex on Fire' and Lady GaGa is at 14 with 'Poker Face'.
Further down the chart Leona Lewis is at 21 with 'Bleeding Love', Atomic Kitten are at 26 with 'Whole Again' and Take That's 'Rule The World' is at 39.
Radio 1 announced the full Top 150 best-selling singles of the 21st Century so far yesterday (May 7), with Reggie Yates, Fearne Cotton, Scott Mills and Greg James going through the countdown across the day.
The Top 20 best-selling singles of the 21st century are as follows:
1. Will Young: 'Anything Is Possible'/'Evergreen'
2. Adele: 'Someone Like You'
3. Gareth Gates: 'Unchained Melody'
4. Black Eyed Peas: 'I Gotta Feeling'
5. Shaggy ft. RikRok: 'It Wasn't Me'
6. Maroon 5 ft. Christina Aguilera: 'Moves Like Jagger'
7. Tony Christie ft. Peter Kay: '(Is This The Way To) Amarillo'
8. Alexandra Burke: 'Hallelujah'
9. Kings of Leon: 'Sex on Fire'
10. Band Aid 20: 'Do They Know It's Christmas?'
11. Kylie Minogue: 'Can't Get You Out Of My Head'
12. Bruno Mars: 'Just The Way You Are'
13. Rihanna ft. Calvin Harris: 'We Found Love'
14. Lady GaGa: 'Poker Face'
15. Shayne Ward: 'That's My Goal'
16. LMFAO: 'Party Rock Anthem'
17. Hear'Say: 'Pure and Simple'
18. Jessie J ft. B.o.B: 'Price Tag'
19. Eminem ft. Rihanna: 'Love The Way You Lie'
20. Rihanna: 'Only Girl (In The World)'
Watch the music video for Will Young's 'Evergreen' below: