My Ariston LS 601 door locked shut during normal loading between cycles and was successfully opened using the top curve of a metal coat-hanger.
[Running a wash programme would not release it, indicating a physical problem]
Make a small hook bend at the tip of the metal end and insert in under the door handle whilst pulling the handle as if to open. Feeling around "blind" for 10 mins or so you will locate the mechanism for release.
Then it's easy to unscrew the metal interior to the door to gain access to release the control panel at the top of the door along with the handle/lock.
A small piece of the plastic mechanism had snapped on mine and the whole moulded unit is removed for repair/replacement.
Paul Morgan, January 2006