Props and motors are correct - Air blowing down.
ESC was calibrated - Motors start/stop at same time
The controller looks healthy, virtual horizon shows correct pitch,yaw and roll direction.
Battery is mounted under bottom plate at center of mass. The quad feels balanced
Taking off on both concrete and grass surfaces.
Can provide any pictures or video that are required!
APM and quad are level (APM is on soft anti-vibration mounts), Props and motors are level with each other.
After research I believe this is a simple issue of PID tuning as my APM is mounted below the motors. I am using APM planner 2 on OSX that does not seem to allow the viewing of the tlogs, however I have attached the tlog but can not verify if it contains useful information
For future viewers:
This turned out to be a typical newbie mistake. Motors 2 and 3 signal wires were crossed so the APM was commanding the wrong motor in order to correct the pitch, resulting in flip.