Hi Shaz,


 
I have just had the same problem and the fix took around three minutes to fix, however from what I read in your posts it sound like the same issue I was having. 
 
Here is what I found. 
The door locking mechanism seems to be moved side to side when the door is locked and unlocked. There is a little spring that holds the whole mechanism up and in place. What happens is that spring is made of a rubbish matterial (my opinion) and tends to rust and break dropping the whole mechanism bellow the actual door latch so it will not when unlocked push down on the latch release. 
 
I used a piece of wire with a hook on the end to go between the glass and the outside door frame and lifted the mechanism just enough to move it over the release latch. Opened the door removed the card and found the broken spring. For the short term I just bent another part of the sprint and stretched it over the latch mechanism and guess what the door was as good as new. 
 
Please note I say that this might not fix your issue but this is what I have found on both of my Mr2's :)
 
Hope this helps.