The band's latest offering knocks the Glee cast's first soundtrack release down to second position following its three-week reign at number one.
Paolo Nutini's Sunny Side Up drops one spot to third, while Gorillaz's new disc Plastic Beach lands at fourth.
Michael Bublé's Crazy Love falls one place to grab the remaining position in the top five.
The top ten albums in full (click where possible for our reviews):
1. (-) Boyzone: 'Brother'
2. (1) Glee Cast: 'Glee: The Music, Volume I'
3. (2) Paolo Nutini: 'Sunny Side Up'
4. (-) Gorillaz: 'Plastic Beach'
5. (4) Michael Bublé: 'Crazy Love'
6. (3) Florence and the Machine: 'Lungs'
7. (6) Lady GaGa: 'The Fame Monster'
8. (5) Mumford & Sons: 'Sigh No More'
9. (15) Andre Rieu: 'Forever Vienna'
10. (11) Alicia Keys: 'The Element Of Freedom'