Had a similar problem with Mondeo MK3, key would not open the bonnet,
turn first to the left then to the right, just not engaging, no access to spring the mechanism from underneath the car, so assuming the Focus is the same locking method as the Mondeo....first swing the badge open, then using an electric drill, chain drill a series of small holes in an oval shape, join them together by using a larger drill, then break out the piece of plastic, you will then expose the lock, its held in by two shear headed bolts.
center pop the heads of each, then with a new 6mm drill drill them out, you will need to use a lot of pressure and cutting fluid will help, it's vital the drill is kept central to the bolt and not allowed to wander, once both bolt heads have been drilled out, the lock will just pull out, (replacement shear head bolts cost about two quid).
when the lock is removed you will find a plastic distance piece one end has a recess the other end a + cross like a screwdriver point, in fact if you have a very long screwdriver this can be used to open the bonnet catch.
I know this sounds long winded but it becomes apparent when actually doing the job.
Wotan (has last laugh)
Wotan