Has the S4 UK just upgraded itself?
I've just rebooted my S4 this morning because it wasn't connecting to the mobile network. After the reboot, my lock screen had reset to the default Samsung screen and not my own picture and the Facebook app needed the password and sync settings re-entering.
Thing is, I don't know what version I was on before. It says the current version is: 4.2.2.
I'm assuming not, it's just strange behavior...