Update.
After some thought and a lot of function checking I have nailed it down to the automatic door locking function which activates when the car reaches about 20 mph is what's causing the issue, I unlocked the car and the hatch opened normally, I then left the car for 30 minutes unlocked and hatch opened normally, I then started the car and reversed down the drive and back up to parking position put car into park switched off engine and the hatch worked normally, then took the car out and returned home (doors auto locked) and the hatch would not open until I locked the car and unlocked it using the key fob or button on the dash.
Not sure if this is normal or not, are their any other RX400h owners who are experiencing this?