Update: After starting to become more and more desperate, not wanting to pay to get it fixed, I tried to with force turning the key longer than it would allow me to - in an attempt to break the lock again.
While doing this, the door unlocked.
The key didn't turn enough to be able to pull it out after unlocking, but I was able to open the door to remove the lock.
In an hour or so I will be getting my new lock, this time for right hand drive cars...