I actually had this problem about two weeks ago with a Puma i bought as a project car, the battery had died after id deadlocked it a few days earlier, i noticed that the actual metal key didn't go fully into the drivers side but did on the passenger side and the boot. turning the key in the boot did nothing but the passenger door made the interior handle move slightly, after an hour of looking like i was trying to break into a car, i found a thread on a ford forum that said the locks were prone to rusting due to lack of use (mainly using the remote fob to open) so i used a little bit of WD40 directly into the lock hole on the passenger door and kept turning the key, eventually after repeating this method the passenger door unlocked completely and i could jump start the car.
I hope this helps