Central Locking not locking

[Yendor]

Hi Folks.
I have a 2006 ST 3.0TD auto with 92K that has spent its life to date on top of a coal mine. Dust everywhere!!! Every day.

When I press the central locking button on my remote to lock the door, I can hear a 'clunk' (as I expect with central locking). However, NONE of the doors lock.
Looking inside the vehicle, all the lock buttons on the inside door handles are constantly in the 'locked' position - and seem stuck in the locked position ('cause I can't manually move the lock tab to 'Open'.

Might I have just 1 central problem - or might I have a problem with each door/lock (x5)?

Advice appreciated.
Thanks

Can you open and close all doors or are they all locked shut?

Were you able to source a key for the driver side door lock?