Just watched the second season of this. Its a pretty cool drama which follows John Mercer, an ex-British special forces soldier arrested by police after he killed his aunt and uncle following his discharge from the military. He is recruited from prison to serve in a covert police squad as a government-backed assassin responsible for eliminating criminals and renegade police officers that the law cannot apprehend.

There's only been two series[seasons] of 6 episodes, the first of which I would think is on DVD.