Beechcraft Duchess Model 76 on a climb out at Bournemouth. The door has popped open on me three times in the past - but all on the take-off roll and I was able to abort the take off. This time - on a climb out and AFTER the gears retracted!!... no possibility of landing back on the remaining runway - would have been taken up by the gear deployment time and not to mention, I was already doing 100kts IAS (no way to slow down that quickly).... Aviate: aircraft is fine - lots of noise, and some aerodynamic differences, but engines are well and nothing is wrong, fly the aircraft; Navigate: Left Hand Circuit best (right door open), spacial awareness of airborne traffic by listening in before takeoff and during the emergency; Communicate: TELL ATC what I intend to do. Always FLY the aircraft. The biggest problem with having an airborne incident (a door pop open) is being distracted from flying the airplane. Remove the 'distraction' by moving my things away from the P2 seat. All DONE - my objective after the door opens is to land, shut the door properly, then go on my merry way. Fly a tight circuit, but otherwise, normal ops to land!!... Just like flying a Tiger Moth, but faster... hehe....