According to a post in Biomechanichal's website(John K's other band), he decided to left the band to dedicate to Biomechanical. The following is a message from John:

"There was no other way than to leave Balance of Power, I feel i have to give Biomechanical 100% of my efforts.
Even 99% is simply not good enough and I feel splitting my energy between two bands creates an inevitable lack of commiment. It's not fair on the guys of Balance of Power to have a singer who can't really commit and also not fair on Biomechanical when I have to take time out in order to rehearse or tour with Balance of Power.
Biomechanical now have the full support of the entire team from Earache/Elitist records and at this point it would be wrong of me not to give everything I have to my band.
It was a great experience working with Balance of Power and I do think they are a very accomplished band with polished albums and very good writing in the melodic Metal genre.
Certainly the best UK band of their style! I know they now have a new vocalist and I'm sure they will continue to have a great success. I wish them all the best for the future!"

Source:	biomechanical.co.uk
Band profile:	Balance Of Power