Driver's door latch not engaging
 

Hi,
I have a 2008 LR2, and as of yesterday, out of the blue, the drivers door will not stay closed when driving. Got in yesterday and had to drive home, holding door closed. The latch is simply not engaging. Within the inside handle, there is the little knob thing which is in the open position, and I can not push it in either.
When I got out of the car, pushed the door closed and used remote to lock, this worked.
Any suggestions would be much appreciated, Thanks.