Just got the same problem today. Fine last time I used it; just failed for no obvious reason.
I had this happen on my previous Panda Cross and had to have a new lock fitted by a local body shop. Cost over £200
If changing the lock yourself be careful to order one for the correct side.
If anyone knows any easier way of fixing the faulty lock I (and Rok52) would be very grateful.
Just taking the interior door trim off is not an easy matter.