Locked lock

This is our back door lock, it is keyed the same as the kitchen door lock, except on Wednesday night last week it wouldn’t unlock. The thief resistance indicated that getting the door open was likely to cause a mess.
However today I ground the ends off the hinge pins, drove them out and lifted the door out of the frame.
As soon as the lock was removed from the door it worked fine.
Just a little grease on the rotating bits and easing of a step in the receiver plate caused by wear.
Saved a lot of replacement costs.