Faulty door lock

2002 TD5 - Key remote locks all doors and opens all doors apart from the driver's door. Then if you just use the key to manually open the driver's door the alarm goes off. Found a way round it by pressing the door open function on the remote after releasing the lock manually but any ideas what is causing this and how to resolve?

Unlocking with the key will set the alarm off, as the system has voltage drop sensoring.
Your problem is the unlocking actuator in the drivers door lock being faulty, common issue so search the Forum for more info, time for a replacement lock.

+1^^^ get a new door latch assy...untill then first unlock with fob then with the key

.... and now my D2 is showing the same symptoms - The driver's door won't unlock via the fob, but it will lock. Would it still require a new latch, or just a clean up seeing as it still works one way? (Somehow I think I know the answer....)

I've set the alarm to always disarm with key in case she ever goes really wrong

As you said, you know the answer (99% new lock)

I have a spare used latch in the garage if either of you want it cheap.

Just had mine done at the garage. Thanks for the offer though.