Hamilton started the band as a side project in 2002, and despite British Sea Power's recent chart success, he has decided to concentrate on Brakes.
A statement from British Sea Power reads, "Due to the ongoing success of his other band, Brakes, BSP keyboardist Eamon has now left BSP to pursue Brakes glory full-time. All remains fully amicable between the five men of BSP past and present.
"Further, it is not unlikely that Eamon will return for the BSP headlining slot at Glastonbury 2007. In the meantime we all wish him well.
"Of course, Eamon's departure creates the most exciting vacancy in rock since 1998. BSP will soon announce a nationwide series of open auditions for the post, while early frontrunners for the job include Charlotte Church."