Its a door that is rarely used so not urgent.
Tried to unlock it and key would only turn about a quarter then jam.
tried all sorts of jiggling and a bit of force....no joy.
Next I tried snapping the lock, I wouldnt make a good housebreaker as it
took me an hour.

I am aware that it is the cam on the euro cylinder that operates the
mechanism and I used the cam on the end of a screwdriver but again a
partial turn and stop!

I have come to the conclusion that something in the door locking
mechanism has broken or jammed and was nothing to do with the euro lock.

My problem is the door is in locked mode so currently cannot access the
lock mechanism, within the `keyhole` I can see a metal piece that I
suspect the key cam would engage, but it wont budge.(it is difficult to
see properly)

So looks like I need to attempt to unscrew the hinges and hope I can get
the door off. (when the weather is better)

Any thoughts or ideas on this.