I can close the drivers door ok but I can only open it from the inside handle. Took the door card off and it appears that the bar linking the handle to the locking mechanism is adrift. However I cant see much because of where it is located. Will removing the outside handle give me any further insight into the problem or does it sound like a new locking mechanism - if available?

Yes it should give you a better view and as its only held on by 2 x 10mm bolts it would be mad not to check and see.